Seed germinations react to their local growing conditions, but the impacts of soil heterogeneity on seed germinations are not well known.

Effects of three-dimensional soil heterogeneity on seed germinations of grasses species were explored, where two levels of such soil heterogeneity were created via alternatively filling nutrient-poor and nutrient-rich substrate in pot in all directions. Patch sizes of the two heterogeneity levels are around 7.5 and 15 cm, respectively. Fifty seeds of each of the grasses species (Lolium perenne and Elymus nutans) were set either in these heterogeneous soils or in petri dishes with distilled water. Seed germinations of these species were daily recorded.

We found that pots with smaller patches had relatively lower germination rate, which is consistent with our expectation that shorter distance between nutrient-rich and nutrient-poor patches in pots with smaller patches allows plants to reduce their germination rates and delay their germination, in order to reduce the negative impacts of the strong variation of soil resources in these pots. Our results also revealed that pots with smaller patches yielded more heterogeneous seed germination, i.e. seed germinations highly diverged among these pots. These findings highlight that the realistic three-dimensional design can improve our understanding of seed germination as driven by soil spatial heterogeneity.

Prediction of changes in ecosystem gross primary productivity (GPP) in response to climatic variability is a core mission in the field of global change ecology. However, it remains a big challenge for the model community to reproduce the interannual variation (IAV) of GPP in arid ecosystems. Accurate estimates of soil water content (SWC) and GPP sensitivity to SWC are the two most critical aspects for predicting the IAV of GPP in arid ecosystems.

We took a widely used model Biome-BGC as an example, to improve the model performances in a temperate grassland ecosystem. Firstly, we updated the estimation of SWC by modifying modules of evapotranspiration, SWC vertical profile and field capacity. Secondly, we modified the function of controlling water–nitrogen relation, which regulates the GPP–SWC sensitivity.

The original Biome-BGC overestimated the SWC and underestimated the IAV of GPP sensitivity, resulting in lower IAV of GPP than the observations, e.g. it largely underestimated the reduction of GPP in drought years. In comparison, the modified model accurately reproduced the observed seasonal and IAVs in SWC, especially in the surface layer. Simulated GPP–SWC sensitivity was also enhanced and became closer to the observations by optimizing parameter controlling nitrogen mineralization. Consequently, the model’s capability of reproducing IAV of GPP has been largely improved by the modifications. Our results demonstrate that SWC in the surface layer and the consequent effects on nitrogen availability should be among the first considerations for accurate modeling IAV of GPP in arid ecosystems.

In a large dam-regulated reservoir with regular hydrological pattern and strong flooding gradients across shore elevations, plants inhabiting in different shore elevations have to confront long-lasting flooding of differential intensities every year. Such persistent stress may lead to intraspecific differentiation of flooding tolerance in seeds. Echinochloa crusgalli var. zelayensis is a dominant annual plant in the shores of the Three Gorges Reservoir (TGR), which plays an important role in the shore vegetation. The objective of this study is to check whether intraspecific differentiation of seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores and whether such differentiation is associated with weak seed dispersal.

We collected seeds of E. crusgalli var. zelayensis from different populations in the TGR shores, and then placed them at four elevations in the shores flooded by reservoir impoundment. Parameters reflecting seed flooding tolerance including post-flooding percentage of intact seeds, seed germinability and seedling emergence rate were investigated for the seeds from different populations and undergoing flooding of different intensities. Floating time of seeds and speed of water level rise during impoundment were examined, and used to quantify dispersal potential of seeds in the shores of the TGR when flooded.

Both intact seed percentage and final seedling emergence rate after flooding significantly declined with increasing shore elevations where the seeds were collected, indicating that intraspecific differentiation in seed flooding tolerance has occurred among E. crusgalli var. zelayensis populations in the TGR shores after 7-year operation of the reservoir. The distance of seeds transported by rising water during reservoir impoundment was limited due to short-floating time of the seeds and relatively low speed of water level rise in the reservoir. This would be favourable to the development of intraspecific differentiation in seed flooding tolerance.

Soil biota can affect plant–plant interactions and non-native plant invasions via plant–soil feedback (PSF). Understanding the drivers underlying interspecific variations in PSF is important for predicting the role of soil biota in non-native plant invasions. Recent studies found that PSF could be predicted by plant traits. The success of plant invasions is also linked with plant traits, suggesting a potential linkage between PSF and plant invasion via plant traits, but has not yet been tested. Here, we compared PSF between six phylogenetically paired co-occurring native and invasive plants, and explored the potential linkage between PSF with plant root traits.

We conducted a two-phase PSF experiment. Field collected soils were conditioned by the six plant species for 3 months firstly, then seedlings of these plants were grown in living or sterilized soils that had been conditioned by conspecific vs. heterospecific (the congener/confamilial species) individuals. We estimated effects of biota in conspecific (conspecific PSF) or heterospecific (heterospecific PSF) soils relative to sterilized soils, and the relative effects of biota in conspecific vs. heterospecific soils (PSF-away) on plant biomass.

In general, soil biota suppressed plant growth, and there were no differences in conspecific PSF, heterospecific PSF and PSF-away between native and invasive plants. PSF increased with rising plant fine-to-total root mass ratio in the presence of soil biota, and its value was comparable between native and invasive plants. Our results indicate that similarity in plant fine-to-total root mass ratio that predicted PSF may have partially led to the comparable PSFs between these native and invasive plants. Studies exploring the linkages among plant traits, PSF and plant invasions with more plants, in particular phylogenetically distant plants, are needed to improve our understanding of the role of soil biota in plant invasions.

Nutrient resorption is a key plant nutrient conservation strategy, and its response to environmental and management changes is linked to nutrient cycling and production of ecosystems. Defoliation is a major pathway of mowing affecting plant nutrient resorption and production in grasslands, while the effect of defoliation timing has not been unexplored. The aim of this study was to examine the effect of defoliation timing on plant nutrient resorption and production in a steppe ecosystem.

We conducted a field experiment in a semi-arid steppe of Inner Mongolia including four treatments: early defoliation, peak defoliation, late defoliation and non-defoliation. We measured plant nitrogen (N) and phosphorus (P) resorption at species and community levels, and quantified plant N and P fluxes in resorption, litter return and hay output. Plant production in the mowing system was assessed by hay production and quality.

Peak and late defoliation, but not early defoliation, reduced plant community N and P resorption proficiency; and late defoliation reduced N resorption efficiency but not P resorption efficiency. Peak and late defoliation, but not early defoliation, reduced plant nutrient resorption flux and litter nutrient return flux. Defoliation timing did not alter root nutrient accumulation as nutrient uptake from soil likely compensated the deficit of nutrient resorption. Peak defoliation had the highest hay production and quality, while early defoliation had the lowest. Our results provide new insights into the nutrient cycling in mowing grassland, and imply that the mowing timing can be used as a tool to mediate the balance between conservation and production of steppes, and the early mowing before plant peak biomass period is recommended for conservation of the steppes while keeping sustainable pastoral production.

Nutrient resorption is a crucial component of plant nutrient use strategy, yet the controls on the responses of community-level nutrient resorption to altered nutrient availability remain unclear. Here, we addressed two questions: (1) Did leaf and stem nutrient resorption respond consistently to increased nutrient availability? (2) Was community-level plant nutrient resorption response after nutrient enrichment driven by the intraspecific plasticity in plant nutrient resorption or by altered species composition?

We investigated the changes in aboveground biomass, and leaf and stem nutrient resorption of individual species after 3-year nitrogen (N) and phosphorus (P) additions, and assessed community-level nutrient resorption response to 3-year nutrient additions in a graminoid-dominated temperate wetland, Northeast China.

For both leaves and stems, N and P additions did not affect nutrient resorption efficiency, but they decreased respective nutrient resorption proficiency. Similarly, community-level N and P resorption proficiency declined with respective nutrient addition. Community-level N and P resorption efficiency was reduced by N addition primarily due to altered community composition and declined leaf:stem ratio. These results suggest that leaf and stem nutrient resorption processes exhibit consistent responses to increasing nutrient availability in the temperate wetland. These findings highlight the importance of altered species composition and biomass allocation between leaf and stem in driving community-level nutrient resorption response to nutrient enrichment.

Leaf size and shape as objects of natural selection can play adaptive roles, and can change with the age of leaves. They can differ between sexes in dioecious species, and in most cases, females have larger leaves. Previous studies showed that sexes of Adriana tomentosa differed in their leaf lobing. In this study, we investigated whether there were other differences between sexes in leaf size, shape and ecophysiology, and if those differences were connected with adaptations and reproductive roles in the sexes of A. tomentosa.

Physical and chemical features of young and old leaves originating from female and male A. tomentosa plants growing in two disjunct populations in eastern Australia were measured. We determined leaf area, perimeter length, serration, circularity, aspect ratio (AR), roundness and the ecophysiological factors: specific leaf area, dry matter content, leaf moisture, relative water content, δ 13C, δ 15N isotope compositions, carbon and nitrogen contents and C:N ratio. Leaf lobing, the degree of lamina damage and the content of photosynthetic pigments were also determined.

In both populations studied, the sex of plants significantly influenced almost all parameters connected with leaf morphology such as area, perimeter length, circularity, AR and roundness. Contrary to expectations, males from both populations had a greater leaf area that was independent of leaf age. Male leaves were more lobed with a longer perimeter, but they were less elongated and less serrated. Only small differences between female and male leaves were observed for the ecophysiological factors. The degree of leaf damage differed between sexes but also with population. Differences between sexes in leaf area and shape were not compensated by measured ecophysiological factors. However, leaf area may be compensated by other ecophysiological mechanisms related to leaf morphology, because females had greater leaf serration in comparison to males despite the smaller leaf area.

Projections of invasive species expansion under a warmer world often do not explicitly consider the concurring nitrogen (N) deposition. It remains largely unknown how the convoluted effect of climate warming and N deposition will shift the native and invasive species dynamics. Here, we hypothesize that the concurring increases in N and temperature would promote growth of invasive species greater than that of native species.

A controlled greenhouse experiment was conducted to quantify the growth response of an invasive species (Solidago canadensis L.) and a co-existing native species (Artemisia argyi Levl. et Van) under the effects of climate warming, N deposition and their interactions.

Due to the strong positive effect of N addition, the interactive effect of temperature increase and N addition resulted in an overall significant increase in growth of both invasive and native species, demonstrating that these manipulations may make microhabitats more favorable to plant growth. However, the relative increases in biomass, height and diameter of invasive S. canadensis were significantly lower than those of native A. argyi. This suggests that the vegetative growth superiority of invasive S. canadensis over the native species A. argyi is reduced by the enhanced N availability in the warmer world. Therefore, the inclusion of N deposition may mitigate the projection of invasive species S. canadensis expansion under climate warming.

Phylogenetic diversity metrics can discern the relative contributions of ecological and evolutionary processes associated with the assembly of plant communities. However, the magnitude of the potential variation associated with phylogenetic methodologies, and its effect on estimates of phylogenetic diversity, remains poorly understood. Here, we assess how sources of variation associated with estimates of phylogenetic diversity can potentially affect our understanding of plant community structure for a series of temperate forest plots in China.

In total, 20 forest plots, comprising of 274 woody species and 581 herbaceous species, were surveyed and sampled along an elevational gradient of 2800 m on Taibai Mountain, China. We used multi-model inference to search for the most parsimonious relationship between estimates of phylogenetic diversity and each of four predictors (i.e. type of phylogenetic reconstruction method, phylogenetic diversity metric, woody or herbaceous growth form and elevation), and their pairwise interactions.

There was no significant difference in patterns of phylogenetic diversity when using synthesis-based vs. molecular-based phylogenetic methods. Results showed that elevation, the type of phylogenetic diversity metric, growth form and their interactions, accounted for >44% of the variance in our estimates of phylogenetic diversity. In general, phylogenetic diversity decreased with increasing elevation; however, the trend was weaker for herbaceous plants than for woody plants. Moreover, the three phylogenetic diversity metrics showed consistent patterns (i.e. clustered) across the elevational gradient for woody plants. For herbaceous plants, the mean pairwise distance showed a random distribution over the gradient. These results suggest that a better understanding of temperate forest community structure can be obtained when estimates of phylogenetic diversity include methodological and environmental sources of variation.

Linkages formed through aquatic–terrestrial subsidies can play an important role in structuring communities and mediating ecosystem functions. Aquatic–terrestrial subsidies may be especially important in nutrient-poor ecosystems, such as the freshwater sand dunes surrounding Lake Michigan. Adult midges emerge from Lake Michigan in the spring, swarm to mate and die. Their carcasses form mounds at the base of plants, where they may increase plant productivity through their nutrient inputs. However, the effect of aquatic–terrestrial subsidies on plant productivity could depend on other biotic interactions. In particular, soil microbes might play a key role in facilitating the conversion of nutrients to plant-available forms or competing for the nutrients with plants.

In a greenhouse experiment, we tested how carcasses from lake emergent midges (Chironomidae) and soil microbes independently and interactively influenced the performance of a common dune grass, Calamovilfa longifolia. To determine whether midges influenced abiotic soil properties, we measured how midge additions influenced soil nutrients and soil moisture.

Midges greatly increased plant biomass, while soil microbes influenced the magnitude of this effect. In the absence of soil microbes plant biomass was seven times greater with midges than without midges. However, in the presence of soil microbes, plant biomass was only three times greater. The effect of midges might be driven by their nutrient inputs into the soil, as midges contained 100 times more N, 10 times more P and 150 times more K than dune soils did. Our results suggest that soil microbes may be competing with plants for these nutrients. In sum, we found that midges can be an important aquatic–terrestrial subsidy that produces strong, positive effects on plant productivity along the shorelines of Lake Michigan, but that the impact of aquatic–terrestrial subsidies must be considered within the context of the complex interactions that take place within ecological communities.

In plant eco-physiology, less negative (enriched) carbon 13 (13C) in the leaves indicates conditions of reducing leaf gas exchange through stomata, e.g. under drought. In addition, 13C is expected to be less negative in non-photosynthetic tissues as compared with leaves. However, these relationships in δ 13C from leaves (photosynthetic organs) to branches, stems and roots (non-photosynthetic organs) are rarely tested across multiple closely related tree species, multiple compartments, or in trees growing under extreme heat and drought.

We measured leaf-to-root 13C in three closely related desert acacia species (Acacia tortilis, A. raddiana and A. pachyceras). We measured δ 13C in leaf tissues from mature trees in southern Israel. In parallel, a 7-year irrigation experiment with 0.5, 1.0 or 4.0 L day−1 was conducted in an experimental orchard. At the end of the experiment, growth parameters and δ 13C were measured in leaves, branches, stems and roots.

The δ 13C in leaf tissues sampled from mature trees was ca. −27‰, far more depleted than expected from a desert tree growing in one of the Earth’s driest and hottest environments. Across acacia species and compartments, δ 13C was not enriched at all irrigation levels (−28‰ to ca. −27‰), confirming our measurements in the mature trees. Among compartments, leaf δ 13C was unexpectedly similar to branch and root δ 13C, and surprisingly, even less negative than stem δ 13C. The highly depleted leaf δ 13C suggests that these trees have high stomatal gas exchange, despite growing in extremely dry habitats. The lack of δ 13C enrichment in non-photosynthetic tissues might be related to the seasonal coupling of growth of leaves and heterotrophic tissues.

In species with morphophysiological seed dormancy (MPD), little is known about the effects of desiccation of imbibed seeds on embryo growth and germination. We studied seed responses to dehydration in nine species with different levels of MPD.

For each species, a control test was conducted by keeping seeds permanently hydrated and exposed to the optimal stratification–incubation sequence to promote embryo growth. Simultaneously, tests were run in which seed stratification was interrupted for 1 month by desiccation at room temperature.

In Clematis vitalba and Ribes alpinum, with nondeep simple MPD, desiccation affected neither embryo growth nor seed viability, but the desiccation led to a decrease of germinative ability in R. alpinum by 16%. The seeds of Narcissus pseudonarcissus subsp. munozii-garmendiae, with deep simple epicotyl MPD, tolerated desiccation in different embryo growth stages, but their germinative ability decreased slightly. The response of species with complex levels of MPD to desiccation was more variable: Delphinium fissum subsp. sordidum, with intermediate complex MPD, and Anthriscus sylvestris and Meum athamanticum, both with deep complex MPD, tolerated desiccation. In contrast, Ribes uva-crispa with nondeep complex MPD, Lonicera pyrenaica with intermediate complex MPD and Chaerophyllum aureum with deep complex MPD, had diminished germination ability by desiccation. Although seeds of the species with simple levels of MPD tolerated desiccation, those of some species with complex levels were also highly tolerant. Thus, desiccation did not induce secondary dormancy in late embryo growth stages. The desiccation tolerance of imbibed seeds of most of the nine species may show their adaptability to climate change in the Mediterranean region.

Competition, temperature and nutrient are the most important determinants of tree growth in the cold climate on the eastern Tibetan Plateau. Although many studies have reported their individual effects on tree growth, little is known about how the interactions of competition with fertilization and temperature affect root growth. We aim to test whether climate warming and fertilization promote competition and to explore the functional strategies of Picea asperata in response to the interactions of these factors.

We conducted a paired experiment including competition and non-competition treatments under elevated temperature (ET) and fertilization. We measured root traits, including the root tip number over the root surface (RTRS), the root branching events over the root surface (RBRS), the specific root length (SRL), the specific root area (SRA), the total fine root length and area (RL and RA), the root tips (RTs) and root branching (RB) events. These root traits are considered to be indicators of plant resource uptake capacity and root growth. The root biomass and the nutrient concentrations in the roots were also determined.

The results indicated that ET, fertilization and competition individually enhanced the nitrogen (N) and potassium (K) concentrations in fine roots, but they did not affect fine root biomass or root traits, including RL, RT, RA and RB. However, both temperature and fertilization, as well as their interaction, interacting with competition increased RL, RA, RT, RB and nutrient uptake. In addition, the SRL, SRA, RTRS and RBRS decreased under fertilization, the interaction between temperature and competition decreased SRL and SRA, while the other parameters were not affected by temperature or competition. These results indicate that P. asperata maintains a conservative nutrient strategy in response to competition, climate warming, fertilization and their interactions. Our results improve our understanding of the physiological and ecological adaptability of trees to global change.

Exposure of Eucalyptus tree stems to the radiant heat of forest fires can kill cambial cells and their embedded regenerative meristems, thus preventing epicormic resprouting and recovery of the tree. Currently, there is no tissue-level method to quantify the viability of cambial cells in Eucalyptus following heat exposure. The first aim of this study was to adapt and validate the tetrazolium reduction method of testing for cell viability in Eucalyptus. The second aim was to apply the method to establish a threshold level of cambium cell viability in Eucalyptus obliqua to enable the identification of a critical temperature.

The study used the tetrazolium reduction method to quantitatively determine phloem–cambium cell viability in Eucalyptus. Circular sections of bark with underlying phloem and cambium were cut from mature E. obliqua and samples ranging in mass from 1 to 30 mg were exposed for 1 min to temperature treatments ranging from 20 to 85 °C and kept for 20–22 h at room temperature in 0.8% 2,3,5-triphenyl tetrazolium chloride (TTC) to test for cell viability. The 1,3,5-triphenyl tetrazolium formazan (TPF) formed was cold extracted with ethanol and quantified as absorbance at 485 nm.

The TTC reduction method reliably quantified a decline in cell viability with rising temperature in tissue sections that included vascular cambium, and identified 60 °C as the critical temperature for cambium–phloem cells of Eucalyptus species. Cell viability, calculated as [TPF Treatment °C]/[TPF 20 °C], declined by 90% between 20 and 85 °C. The cell viability results confirmed that significant tissue necrosis occurred in Eucalyptus at temperatures between 50 and 70 °C, after 1 min of in vitro tissue heating. The decline in cell viability with increasing temperature shown by the TTC method was consistent with an independently derived count of live cells following temperature treatment and neutral red staining.

The belowground bud bank plays an important role in vegetation restoration of sand dune ecosystems in semi-arid regions. However, few studies have focused on the temporal–spatial changes of belowground bud banks in interdune lowlands.

The size and composition of belowground bud bank in five interdune lowlands with different sizes were investigated for one growing season to determine the temporal and spatial changes in belowground bud bank.

Total bud bank density was the highest in the medium-sized interdune lowland as was tiller bud density. The density of stem-base buds exhibited an opposite trend while rhizome bud density did not change with interdune lowland size. There was a significant seasonal change in the bud bank size. The total bud density peaked in August and was the lowest in October. A similar trend was found for rhizome bud density, whereas the density of stem-base buds showed an opposite trend, and tiller bud density did not change significantly during the growing season. We conclude that the belowground bud bank density is changed with interdune lowland size and season. These results contribute to the understanding of adaptive strategies of plants growing in active dune ecosystems and provide pointers for adopting effective measures to restore and conserve dune vegetation in semi-arid regions.