Aims Boreal larch (Larix gmelinii) forests in Northeast China have been widely disturbed since the 1987 conflagration; however, its long-term effects on the forest carbon (C) cycling have not been explored. The objective of this study thus was to quantify the effects of fire severity and post-fire reforestation on C pools and the changes of these forests.
Methods Sixteen permanent plots have been set in two types of larch stands (L. gmelinii -grass, LG; and L. gmelinii-Rhododendron dahurica, LR) with three levels of fire severity (unburned, low-severity and high-severity but replanted), at 1987 burned sites in Daxing'anling, northeastern China, to repeatedly measure ecosystem C pools in 1998 and 2014. C components were partitioned into vegetation (foliage, branch, stem and roots), soil and detritus (standing and fallen woody debris and litter). The fire effects on post-fire C dynamics were examined by comparing the differences of C pools and changes between the two field investigations caused by fire severity.
Important findings During the study period, unburned mature stands were C sinks (105g C m ?2 year^-1 for LG, and 190g C m ?2 year^-1 for LR), whereas the low-severity stands were C-neutral (?4 and 15g C m ?2 year^-1 for LG and LR, respectively). The high-severity burned but reforested stands were C sinks, among which, however, magnitudes (88 and 16g C m ?2 year^-1 for LG and LR, respectively) were smaller than those of the two unburned stands. Detritus C pools decreased significantly (with a loss ranging from 26 to 38g C m ?2 year^-1) in the burned stands during recent restoration. Soil organic C pools increased slightly in the unmanaged stands (unburned and low-severity, with accumulation rates ranging from 4 to 35g C m ?2 year^-1), but decreased for the high-severity replanted stands (loss rates of 28 and 36g C m ?2 year^-1 for LG and LR, respectively). These results indicate that fire severity has a dynamic post-fire effect on both C pools and distributions of the boreal larch forests, and that effective reforestation practice accelerates forest C sequestration.

Aims The aim of this study was to investigate the effects of precipitation changes on soil organic carbon (SOC) fractions in subtropical forests where the precipitation pattern has been altered for decades.
Methods We conducted field manipulations of precipitation, including ambient precipitation as a control (CK), double precipitation (DP) and no precipitation (NP), for 3 years in three forests with different stand ages (broadleaf forest [BF], mixed forest [MF] and pine forest [PF]) in subtropical China. At the end of the experiment, soil samples were collected to assay SOC content, readily oxidizable organic carbon (ROC) and non-readily oxidizable organic carbon (NROC), as well as soil microbial biomass carbon (MBC), pH and total nitrogen content. Samples from the forest floors were also collected to analyze carbon (C) functional groups (i.e. alkyl C, aromatic C, O-alkyl C and carbonyl C). Furthermore, fine root biomass was measured periodically throughout the experiment.
Important findings Among the forests, ROC content did not exhibit any notable differences, while NROC content increased significantly with the stand age. This finding implied that the SOC accumulation observed in these forests resulted from the accumulation of NROC in the soil, a mechanism for SOC accumulation in the mature forests of southern China. Moreover, NP treatment led to significant reductions in both ROC and NROC content and therefore reduced the total SOC content in all of the studied forests. Such decreases may be due to the lower plant-derived C inputs (C quantity) and to the changes in SOC components (C quality) indicated by C functional groups analyses under NP treatment. DP treatment in all the forests also tended to decrease the SOC content, although the decreases were not statistically significant with the exception of SOC and ROC content in PF. This finding indicated that soils in MF and in BF may be more resistant to precipitation increases, possibly due to less water limitations under natural conditions in the two forests. Our results therefore highlight the different responses of SOC and its fractions to precipitation changes among the forests and suggest that further studies are needed to improve our understanding of SOC dynamics in such an important C sink region.

Aims Slash removal is a common practice to prepare recently harvested sites for replanting. However, little is known about its impact on soil carbon (C) dynamics in subtropical plantations. This study evaluates the effects of burning versus manual slash removal site preparation treatments on soil organic carbon (SOC), soil respiration and soil microbial community structure in a Pinus massoniana plantation in southern China.
Methods Three areas within a mature P. massoniana plantation were clearcut. Two months following harvesting, slash on one-half of each area was burned (BURN), whereas slash was manually removed (MANR) on the other portion. Slash removal treatments were also compared with adjacent uncut plantation areas (UNCUT). Soil samples, and soil respiration measurements were used to characterize soil properties and microbial communities following slash removal treatments.
Important findings Mean soil respiration rates from the MANR and BURN treatments were 26% and 17% lower, respectively, than the UNCUT treatment over 1 year. The MANR and BURN treatment resulted in soils with 27% and 9% reduction in total phospholipid fatty acids (PLFAs) and 18% and 10% reduction in bacterial PLFAs, respectively, compared with the UNCUT treatment. However, no significant differences existed between slash removal treatments with respect to soil chemical properties, SOC chemical compositions, soil respiration and microbial communities; although PLFA patterns were notably different for the burned plots. Most factors affecting C dynamics and microbial communities were not sensitive to the differences imparted to the ecosystem due to manual slash removal or burning. Our results suggested that low-intensity burning after clear-cutting might have no significant effect on soil C pool and its dynamics compared with manual slash removal in subtropical plantations.

Aims Resource allocation in plants can be strongly affected by competition. Besides plant–plant interactions, terrestrial plants compete with the soil bacterial community over nutrients. Since the bacterial communities cannot synthesize their own energy sources, they are dependent on external carbon sources. Unlike the effect of overall amounts of carbon (added to the soil) on plant performance, the effect of fine scale temporal variation in soil carbon inputs on the bacterial biomass and its cascading effects on plant growth are largely unknown. We hypothesize that continuous carbon supply (small temporal variance) will result in a relatively constant bacterial biomass that will effectively compete with plants for nutrients. On the other hand, carbon pulses (large temporal variance) are expected to cause oscillations in bacterial biomass, enabling plants temporal escape from competition and possibly enabling increased growth. We thus predicted that continuous carbon supply would increase root allocation at the expense of decreased reproductive output. We also expected this effect to be noticeable only when sufficient nutrients were present in the soil.
Methods Wheat plants were grown for 64 days in pots containing either sterilized or inoculated soils, with or without slow-release fertilizer, subjected to one of the following six carbon treatments: daily (1.5mg glucose), every other day (3mg glucose), 4 days (6mg glucose), 8 days (12mg glucose), 16 days (24mg glucose) and no carbon control.
Important findings Remarkably, carbon pulses (every 2–16 days) led to increased reproductive allocation at the expense of decreased root allocation in plants growing in inoculated soils. Consistent with our prediction, these effects were noticeable only when sufficient nutrients were present in the soil. Furthermore, soil inoculation in plants subjected to low nutrient availability resulted in decreased total plant biomass. We interpret this to mean that when the amount of available nutrients is low, these nutrients are mainly used by the bacterial community. Our results show that temporal variation in soil carbon inputs may play an important role in aboveground–belowground interactions, affecting plant resource allocation.

Aims Central Hungarian inland dune ranges harbor heterogeneous grassland vegetation with an extensive network of ecotones, arranged perpendicular to topography-driven hydrologic gradients. The area suffers from severe aridification due to climate change and local anthropogenic factors, which have led to a dramatic decline of the water table. As a result, groundwater is no longer reachable for low-lying plant communities; thus, we expect they are bound to undergo profound changes. This study investigates how the plant communities respond to this changing environment over time by monitoring ecotones, since they are frequently the hotspots of ecosystem change. We monitored five ecotones along permanent belt transects for 15 years to characterize their dynamic response, and to identify the internal structural changes of the plant communities the ecotones delimit.
Methods Ecotones were delineated with the split moving window technique. The dynamics of two ecotone parameters, location and contrast, were analyzed with linear regression models incorporating two independent variables: study year as a measure of time since the loss of groundwater, and precipitation as a possible driver of inter-annual variations. The internal changes of the patches separated by the ecotones were analyzed using plant functional groups.
Important findings Precipitation had no detectable effect on the ecotone descriptors, but study year influenced ecotones in an unusual fashion. The position of the ecotones appeared to be very stable in time; their dynamics are stationary, not directional as we predicted. The contrasts had clear tendencies; two ecotones disappeared, one new one was formed and two ecotones showed no trend. The internal changes of the patches over time were dramatic, showing a shift toward more xeric and more open plant assemblages in most stretches of the transects. Thus, the dynamic response of the vegetation was not patch expansion vs. shrinking, but fusion vs. division, which profoundly restructured the vegetation pattern. Analysis of plant functional groups revealed that the trends of the ecotone contrasts could be traced back to internal changes of the patches and not to processes within ecotones. Hence, in situations where stationary ecotone dynamics prevail, ecotone position may be a poor indicator of the effects of strong directional environmental changes. However, in this study we show that ecotone contrast can serve as a sensitive tool for monitoring landscape pattern transformations in these cases. Also, this highlights the long-term nature of ecotone responses, which can have implications in landscape planning and restoration measures.

Aims Drought affected by atmosphere–ocean cycle is a dominant factor influencing tree radial growth of sandy Mongolian pine (Pinus sylvestris var. mongolica) and regional vegetation dynamics in Hulunbuir, China. However, historical droughts and its correlations with tree radial growth and atmosphere–ocean cycle in this area have been little tested.
Methods We developed tree-ring chronologies of Mongolian pine from Hulunbuir, Inner Mongolia, China and analyzed the correlations between tree-ring width index, the normalized difference vegetation index and Palmer drought severity index (PDSI), then developed a linear model to reconstruct the drought variability from 1829 to 2009. Long-term trends and its linkages with atmosphere–ocean cycle were performed by the power spectral, wavelet and teleconnection analysis.
Important findings The local moisture variations affected largely the regional vegetation dynamics and tree-ring growth of Mongolia pine in the forest–grassland transition. Using tree-ring width chronology of Mongolian pine, the reconstruction explains 49.2% of PDSI variance during their common data period (1951–2005). The reconstruction gives a broad-scale regional representation of PDSI in the Hulunbuir area, with drought occurrences in the 1850s, 1900s, 1920s, mid-1930s and at the turn of the 21st century. Comparisons with other tree-ring drought reconstructions and historical records reveal some common drought periods and drying trends in recent decades at the northern margin zones of the East Asian summer monsoon (EASM). The drying trends in these zones occurred earlier than weakening of the EASM. A REDFIT spectral analysis shows significant peaks at 7.2, 3.9, 2.7–2.8, 2.4 and 2.2 years with a 0.05 significance level, and 36.9, 18.1 and 5.0 years with 0.1 significance level. Wavelet analysis also shows similar cycles. Drought variations in the study area significantly correlated with sea surface temperatures in the western tropical Pacific Ocean and middle and northern Indian Ocean, and the Pacific Decadal Oscillation and North Atlantic Oscillation. This suggests a possible linkage with the El Ni?o-Southern Oscillation, the EASM and the Westerlies.

Aims Abiotic stresses may interact with each other to determine impacts on plants so that their combined impact is less than or more than additive. Increasing UV-B radiation and surface ozone (O 3) are two major components of global change that may have such interactive impacts. Moreover, invasive and native populations of plants may respond differently to stresses as they can vary in primary and secondary metabolism.
Methods Here, we conducted a factorial field experiment with open-top chambers assigned to an ozone treatment (ambient, 100 ppb, or 150 ppb) and UV-B treatment (ambient or increased 20%). We grew seedlings of native and invasive populations of Triadica sebifera in these chambers for one growing season.
Important findings Invasive plants grew faster than native plants in ambient UV-B but they did not differ significantly in elevated UV-B. Litter production of invasive plants was especially sensitive to UV-B in a way that increased with UV-B for native plants but decreased for invasive plants which may be important for nutrient cycling. In ambient UV-B, total mass decreased as ozone increased. Total mass was lower with elevated UV-B but there was no additional impact of increasing ozone. Leaf area did not decrease with UV-B so SLA and LAR were lowest at ambient ozone levels. These results suggest that the effects of ozone will depend on UV-B conditions perhaps due to changes in foliar traits. The traits that allow invasive populations of plants to be successful invaders may make them especially sensitive to UV-B which may reduce their success in future climatic conditions.

Aims Both dominance distribution of species and the composition of the dominant species determine the distribution of traits within community. Leaf carbon (C) and nitrogen (N) isotopic composition are important leaf traits, and such traits of dominant species are associated with ecosystem C, water and N cycling. Very little is known how dominant species with distinct traits (e.g. N-fixing leguminous and non-leguminous trees) mediate resource utilization of the ecosystems in stressful environment.
Methods Leaves of 81 dominant leguminous and non-leguminous trees were collected in forest (moist semi-deciduous and dry semi-deciduous ecosystems) and savanna (costal savanna, Guinean savanna and west Sudanian savanna ecosystems) areas and the transitional zone (between the forest and the savanna) along the transect from the south to the north of Ghana. We measured leaf traits, i.e. leaf δ 13 C, leaf δ 15 N, leaf water content, leaf mass per area (LMA) and C and N concentration. Correlation analyses were used to examine trait–trait relationships, and relationships of leaf traits with temperature and precipitation. We used analysis of covariance to test the differences in slopes of the linear regressions between legumes and non-legumes.
Important findings Leaf δ 13 C, δ 15 N, leaf water content and LMA did not differ between leguminous and non-leguminous trees. Leaf N concentration and C:N ratio differed between the two groups. Moreover, leaf traits varied significantly among the six ecosystems. δ 13 C values were negatively correlated with annual precipitation and positively correlated with mean annual temperature. In contrast, leaf δ 15 N of non-leguminous trees were positively correlated with annual precipitation and negatively correlated with mean annual temperature. For leguminous trees, such correlations were not significant. We also found significant coordination between leaf traits. However, the slopes of the linear relationships were significantly different between leguminous and non-leguminous trees. Our results indicate that shifts in dominant trees with distinct water-use efficiency were corresponded to the rainfall gradient. Moreover, leguminous trees, those characterized with relative high water-use efficiency in the low rainfall ecosystems, were also corresponded to the relative high N use efficiency. The high proportion of leguminous trees in the savannas is crucial to mitigate nutrient stress.

Aims Mistletoe infection between intra- and interspecific hosts can be restricted by seed dispersal, host–mistletoe compatibility and other factors, yet few studies have linked seed dispersal and seedling establishment together for understanding mistletoe plant distribution and demography together in different anthropogenic disturbance forest types at a local scale. The objectives of this study were to examine how three factors—seed disperser behavior, post-dispersal host compatibility and canopy cover—affect the spatial distribution of a generalist mistletoe Dendrophthoe pentandra (Loranthaceae) in plantation and rainforest within Xishuangbanna, Southwest China.
Methods We observed mistletoe D. pentandra infection patterns at the scale of individual trees and sixteen 400-m 2 forest plots in adjacent plantation and rainforest within Xishuangbanna. To elucidate what determines infection patterns at different scales and in different forest types, we observed the behavior of major avian seed dispersers and carried out a seed inoculation experiment to examine how post-dispersal compatibility and light incidence affect the infection of different hosts.
Important findings Dendrophthoe pentandra displayed an aggregated distribution and infected 10 species in our study site, with a significantly higher infection prevalence and intensity in the plantation than in the tropical forest. Different seed dispersers provided contrasting initial mistletoe templates: the specialist frugivore Dicaeum concolor (plain flowerpecker) preferred to fly between mistletoes in infected trees in the plantation and likely intensified existing infections. In contrast, the dietary generalist Pycnonotus jocosus (red-whiskered bulbul) was more likely to visit uninfected trees, thereby establishing new infections. Thus, seed dispersal appears to be an important determinant of the mistletoes distribution, with deposition patterns providing an initial distribution template and determining small-scale patterns. However, post-dispersal and abiotic factors revealed that different host compatibilities and levels of light incidence in different habitats affected the survival of D. pentandra seedlings. Hence, our findings suggest that seed dispersal interacts with host compatibility and canopy cover to determine establishment success, survival and the observed distribution patterns.

Aims The sedge Kobresia pygmaea is the dominant species of high-altitude pastures in Tibet, and it is the most important source of forage in animal husbandry. We present the first comprehensive reproduction study for this perennial key species that adopts a molecular approach and tests how sexual and vegetative reproduction, as well as ploidy, relate to survival and dominance under harsh conditions.
Methods We assessed inflorescence numbers of K. pygmaea across two Tibetan alpine pastures with differing grazing regimes. Germination was tested in untreated diaspores and then following mechanical and chemical scarification. In a 4-year experiment, we assessed diaspore viability and seed bank formation. Using eight microsatellite markers, we recorded multilocus genotypes in hierarchical grids and measured their ploidy using flow cytometry. Adjusted analysis of variance models were used to analyse data on sexual reproduction, while the complement of the Simpson index and the Shannon diversity index were used to characterize the spatial distribution of multilocus genotypes and clonal richness.
Important findings Inflorescence production was high and differed significantly between years (2010: 617±460 SD; 2012: 2015±1213 SD) but not between grazing regimes. Diaspore viability was high (94%) and gradually decreased after 3 and 4 years of storage in the soil. Diaspores not exposed to further scarification failed to germinate, while mechanical and chemical (H 2 SO 4) scarification increased germination to 9 and 44%, respectively. Clonal diversity was high, although in situ germination was rarely observed. Multilocus genotypes intersected and covered a mean area of 0.74 m 2. Most individuals were found to be tetraploid, with only 0.8% of all ramets being triploid. We conclude that K. pygmaea survives on the Tibetan Plateau by employing a mixed reproduction strategy involving both sexual and clonal propagation. The species' adaptability and dominance is further facilitated by its polyploidy. As pasture restoration using diaspores would be difficult, existing Kobresia pasture should be managed more sustainably.

Aims Theory suggests that species perform best at intermediate densities, where density-dependent facilitation and antagonism are balanced, but empirical evidence is scarce, particularly in plants. In a self-incompatible perennial herb (Saussurea nigrescens), whose recruitment heavily relies on seed output, we test whether both intraspecific facilitation and antagonism significantly affect seed production, resulting in highest seed yield at an intermediate capitulum density.
Methods Plots with different S. nigrescens densities were sampled in an Eastern Tibetan meadow during the growing season of 2012 to investigate the relationships between capitulum density and pollinator visitation rate, seed set ratio, parasite ratio, seed damage ratio, and capitulum size. Both simple linear and quadratic models were employed to determine the shape of relationships.
Important findings In line with general theory, hump-shaped relationships of capitulum density versus seed set ratio and number of florets per capitulum indicate intraspecific facilitation in sparse populations, which can be attributed to positive density-dependent pollinator visitation and the amelioration of detrimental physical factors. However, the proportion of seeds damaged by pre-dispersal predators increased monotonically with capitulum density, which may have—in combination with increased intraspecific competition for light and soil nutrients—resulted in density-dependent antagonism. Both positive and negative density-dependent agents acted simultaneously throughout the density range investigated and led to the highest seed yield at intermediate density levels in the Tibetan lotus. More efforts concurrently exploring the two effects are needed to facilitate understanding species abundance and community structure.

Aims Changes in the phenotype of crops (phenotypic plasticity) are known to play an important role in determining responses to nutrient availability, with the direction and magnitude of plasticity of individual traits being crucial for grain yields. Our study analysed the direction, magnitude and hierarchy of plastic responses of yield-related traits (i.e. biomass allocation and yield components) of rice (Oryza sativa L.) to nutrient availability. We estimated the effect of inoculation with arbuscular mycorrhizal fungi (AMF) on these characteristics of phenotypic plasticity.
Methods A field experiment was carried out in northeast China, providing rice with six NPK fertilizer levels with or without inoculation with Glomus mosseae. At maturity, we quantified biomass allocation traits (shoot:root ratio and panicle:shoot ratio) and yield component traits (panicle number per hill, spikelet number per panicle, percentage of filled spikelets and seed weight). We also assessed the direction of change in each trait and the magnitude of trait plasticity.
Important findings In non-inoculated plants, we found that biomass allocation and seed-number traits (i.e. panicle number per hill, spikelet number per panicle and percentage of filled spikelets) responded to fertilization in the same direction, increasing with rising fertilization. Panicle formation was the most plastic trait, while seed mass was the least plastic trait. AMF inoculation nullified the relationship between most biomass allocation and seed-number traits (except for that between panicle:shoot ratio and the percentage of filled spikelets) but increased the magnitude of plasticity in biomass allocation traits without altering the hierarchy of traits' plasticity. These results underscore the importance of plasticity of yield-related traits per se, and the impact of AMF on plasticity, for maintaining rice yields under low fertilization regimes.