Unmanned aerial vehicles (UAVs), i.e. drones, have recently emerged as cost-effective and flexible tools for acquiring remote sensing data with fine spatial and temporal resolution. It provides a new method and opportunity for plant ecologists to study issues from individual to regional scales. However, as a new method, UAVs remote sensing applications in plant ecology are still challenged. The needs of plant ecology research and the application development of UAVs remote sensing should be better integrated.

This report provides a comprehensive review of UAV-based remote sensing applications in plant ecology to synthesize prospects of applying drones to advance plant ecology research.

Of the 400 references, 59% were published in remote sensing journals rather than in plant ecology journals, reflecting a substantial gap between the interests of remote sensing experts and plant ecologists. Most of the studies focused on UAV remote sensing’s technical aspects, such as data processing and remote sensing inversion, with little attention on answering ecological questions. There were 61% of studies involved community-scale research. RGB and multispectral cameras were the most used sensors (75%). More ecologically meaningful parameters can be extracted from UAV data to better understand the canopy surface irregularity and community heterogeneity, identify geometrical characteristics of canopy gaps and construct canopy chemical assemblies from living vegetation volumes. More cooperation between plant ecologists and remote sensing experts is needed to promote UAV remote sensing in advancing plant ecology research.

To explore whether grazing-induced legacy effects on plants could benefit plants adaptation to drought.

A water-controlled experiment was conducted in the greenhouse, which with Agropyron cristatum and Carex korshinskyi collected from free-grazing and enclosed plots on a typical grassland in Inner Mongolia.

We found that A. cristatum and C. korshinskyi collected from the free-grazing plot were less affected by drought in terms of ramet biomass, ramet number and total biomass than those collected from the enclosed plot. The enhanced adaptation to drought for plants collected from the free-grazing plot should partly be ascribed to the larger root biomass allocation plasticity under drought treatment. Our findings suggest that grazing management can be used to improve the adaptation of grassland plants to climate change.

Both extreme drought and insect herbivores can suppress plant growth in grassland communities. However, most studies have examined extreme drought and insects in isolation, and there is reason to believe that insects might alter the ability of grasslands to withstand drought. Unfortunately, few studies have tested the interactive effects of extreme drought and insect herbivores in grassland communities.

Here, we tested the drought–herbivore interactions using a manipulative experiment that factorially crossed extreme drought with the exclusion of insect herbivores in a temperate semiarid grassland in Inner Mongolia.

Our results demonstrated that both extreme drought and insect herbivores separately decreased total plant cover. When combined, insect herbivores reduced the impact of drought on total cover by increasing the relative abundance of drought-resistant dominant species. Our results highlight that the negative effect of extreme drought on total plant cover could be alleviated by maintaining robust insect herbivore communities.

Dioecious plants present sexual dimorphism, but how the root traits and nutrient uptake of female and male plants in dioecious species response to the sexual identity change of the neighbor plants are poorly understood.

Mulberry (Morus alba L.), a dioecious plant widely distributed in China, was employed in our study. Male and female plants were grown with neighbors of the same and opposite sex for 3 months. At harvest, the root anatomy, root morphology, nutrient concentrations and biomass accumulation were measured.

When grown with the opposite sex, the males showed decreases in root xylem size, biomass of root and stem and increases in root N, P and K concentrations compared with grown with the same sex. By contrast, females showed significant increases in xylem size, fine root system (e.g. fine root length, root surface area and root volume), root carbon isotope composition (δ 13C) and root N, P and K concentrations. The changes in the δ 13C and N, P and K concentrations in male and female plants were associated with the changes of root traits. These results demonstrated that the sexual identity of the neighboring plants affected root anatomy and morphology of female and male mulberry plants. Meanwhile, the responses of female and male plants to the sex change of the neighboring plants showed sexual dimorphism, which influenced water-use efficiency and resource acquisition. These findings are important for understanding the population dynamics of other dioecious species in forestry and natural systems.

Litter is frequently buried in the soil in alpine grasslands due to grassland degradation, serious rodent infestation and frequent strong winds. However, the effects of various litter positions on litter decomposition rates and nutrient dynamics under nitrogen (N) enrichment in such areas remain unknown.

A field experiment was performed in the alpine grasslands of northwest China to investigate the influence of litter position (surface, buried in the soil and standing) and N enrichment on litter decomposition, using data from two dominant grass species (Festuca ovina and Leymus tianschanicus) in control and N-enriched plots.

Litter decomposition rates were much faster in buried litter and slower in standing litter than in surface litter. N enrichment significantly affected litter quality and then influenced decomposition. But no significant differences in litter mass remaining were observed between control and N-enriched soil burial. These results indicated that N enrichment significantly affected litter decomposition by changes in litter quality. In addition, all litter exhibited net carbon (C) and phosphorus (P) release regardless of treatments. Litter exhibited net N accumulation for litter from the control plots but showed N release for litter from N enrichment plots. These suggested that litter decomposition can be limited by N and N enrichment influenced N cycling of litter. Current study presented direct evidence that soil buried litter exhibited faster mass loss and C release, and that soil burial can be a candidate explanation why litter decomposes faster than expected in dryland.

Cunninghamia lanceolata is one of the most important coniferous species in southern China, but its high sensitivity to drought restricts its expansion. Understanding the intraspecific variation of physiological responses to drought can help us manage this plantation better.

We selected 3-year-old seedlings of C. lanceolata, which originated from the low precipitation (LP), middle precipitation (MP) and high precipitation (HP) habitats, respectively. Seedlings were grown under drought stress (20% of soil volumetric water content) for 40 days. The ecophysiological responses and adaptive strategies with different drought tolerance were investigated.

LP provenance possessed the best tolerance to drought stress, suggesting that considerably increased carbohydrates and nitrogen-containing compounds as osmotic protective materials, which were driven by fast carbon and nitrogen metabolisms. In addition, the highest peroxidase activity could effectively eliminate hydrogen peroxide in drought-stressed LP provenance. The MP provenance reserved a large amount of non-structural carbohydrates, which may act as a certain buffer for encountering drought stress. Importantly, timely closure of stomata to reduce needle transpiration when encountering a water deficiency would help them adapt to long-term drought. MP provenance adopted a conservative water-saving strategy. However, HP provenance regulated root growth (increased root/shoot ratio) and reduced penetration potential to help them absorb water. The different strategies among provenances may be related to the long-term domestication of the geographical environments. Therefore, our results underline the importance of provenance-specific responses to drought stress. It is highly significant to accelerate the selection of drought-resistant germplasms and to cultivate high-yield plantations in the future.

In the Oregon of USA, the control of western juniper (Juniperus occidentalis) is an accepted rangeland management practice to restore sagebrush steppe habitats of importance to wildlife and livestock. The effects of juniper cutting on ecosystem nitrogen, however, have not been well addressed although woody plant control has important implications for local watershed management and regional nitrogen pools.

We quantified ecosystem nitrogen stocks in two adjacent watersheds, comprised of a treated watershed (most juniper removed) and an untreated watershed (juniper not removed). Thirteen years after juniper removal, we measured aboveground nitrogen stocks for juniper trees, shrubs, grasses and litter in both watersheds. We also measured belowground nitrogen stocks (roots and soil) in both watersheds at two soil depths (0–25 and 25–50 cm).

Aboveground nitrogen stocks were 6.9 times greater in the untreated than in the treated watershed considering the much larger aboveground biomass. However, root nitrogen stocks were 3.1 times greater in the treated one due to the gain of understory root biomass associated with juniper cutting. Soil nitrogen stocks at both 0–25 and 25–50 cm depths were not affected by juniper removal. Overall, total ecosystem nitrogen stocks did not differ between the treated (9536 kg N ha−1) and untreated (9456 kg N ha−1) watersheds. The greatest ecosystem nitrogen accumulation (at least 95% total ecosystem nitrogen) resided belowground (soil 0–50 cm and roots) in both watersheds. This study provides evidence that the benefits of juniper removal can be attained without significantly affecting the capacity of ecosystem nitrogen storage.

We compared vein and stomatal traits of seedlings and adults of three Mediterranean Quercus species. Previous work suggests that gas-exchange rates tend to be higher at the seedling stage than in adults. Our objective was to determine whether vein and stomatal traits vary throughout whole-plant ontogeny in parallel with the changes in gas-exchange rates. We addressed the following alternative hypotheses: hypothesis 1—seedlings show higher vein and stomatal densities than adults; and hypothesis 2—seedlings have lower investments in vascular tissues to reduce construction costs.

Ten specimens from each growth stage were randomly sampled for each species in a location in central-western Spain. We measured mean stomatal and vein traits (size and number of stomata per unit of leaf area, vein density, vein volume, vein to epidermis distance), leaf mass per area and lamina thickness.

Minor vein density and vein volume per area increased with tree age, which seems inconsistent with the ontogenetic trends in gas-exchange rates. This discrepancy is in support of our hypothesis 2, and it suggests that, at the seedling stage, reducing investments in vascular tissues in benefit of maximizing growth rates is a priority. Larger interveinal distances in seedlings were compensated by smaller vein to epidermis distances. The thin leaves of the seedlings may thus constitute as a necessary trait for achieving shorter path length distances for the transport of water to evaporation sites without the need for a strong investment in costly vascular tissues.

Atmospheric nitrogen (N) deposition influences tree hydraulic architecture and thus the growth and survival; but the responses of leaf hydraulic traits remain uncertain, and may vary with species or plant functional types.

We used the 16-year N addition experiment (10 g N m⁻² year⁻¹) on Fraxinus mandshurica (ash, broadleaf angiosperm) and Larix gmelinii (larch, conifer gymnosperm) plantations in northeastern China and examined the effect of N addition on their leaf hydraulics. We measured the leaf pressure–volume traits by the bench drying method and quantified the maximum leaf hydraulic conductance (K_{leaf_max}) and resistance to embolism (P_50leaf) by the timed rehydration method.

Larch had higher K_{leaf_max} and stronger drought tolerance (i.e., lower relative water content at turgor loss point (RWC_tlp) and modulus of elasticity (ε), and more negative P_50leaf) than ash. N addition increased the leaf osmotic potential at turgor loss (π_tlp) and full turgor (π₀), and leaf capacitance (C_{leaf_mass}) for ash but not for larch, indicating that ash is more sensitive to N addition. N addition consistently increased K_{leaf_max} and P_50leaf values for both species. π_tlp and π₀ were positively while C_{leaf_mass} was negatively correlated with leaf density (LD) for ash. K_{leaf_max} was positively but P_50leaf was negatively related with LD for larch. There were negative relationships between K_{leaf_max} and P_50leaf for both species. Overall, our findings suggest that long-term N addition decreases the leaf drought tolerance for these two important tree species, which improve the understanding of the tree hydraulic performance under N deposition.

Understanding variation and coordination of leaf traits at multiscales along elevational gradients can help predict the likely responses of dominant species to climate change. We seek to determine the extent to which variation in leaf stomatal, anatomical and morphological traits is associated with environmental factors, and whether ecological strategies of Cyclobalanopsis species shift with elevations.

In a tropical forest landscape in Jianfengling, South China, we determined leaf traits related to stomata, anatomy and morphology of six evergreen oak species (Cyclobalanopsis bambusaefolia, C. hui, C. patelliformis, C. fleuryi, C. tiaoloshanica and C. phanera) along a long elevational gradient (400–1400 m above sea level).

We found that stomatal density and stomatal pore index increased, whereas spongy mesophyll thickness to leaf thickness ratios decreased, significantly with elevation. The leaf area and leaf dry matter content increased and decreased, respectively, with elevation. Variations in stomatal, anatomical and morphological traits were mainly correlated to the mean annual temperature, mean annual sum precipitation and soil pH. At low and high elevations, the oak species exhibited strong stress tolerance combined with competition strategy, while they shifted toward more clearly the competitive strategy at intermediate elevations. And the changes in soil phosphorus concentration and soil pH along the elevation may drive the shift of ecological strategy. The results showed that the dominant oak species in tropical forests respond to environmental change by modulating traits at multiple levels, from that of the individual cell, through tissue and up to the whole leaf scale.

Seasonal variations in species richness, aboveground net primary productivity (ANPP) and stability under resource enrichment are frequently ignored. This study explores how the impacts of resource enrichment on species richness, ANPP and stability vary among seasons in semi-arid grasslands.

We conducted a 3-year experiment in an Inner Mongolia grassland to determine the effects of resource input (water [W], nitrogen [N]) on species richness, community ANPP and stability using seasonal sampling during the growing season (2013–2015). Structural equation modeling (SEM) was used to examine the relative importance of resource input on community stability via mechanistic pathways in each month and the whole growing season.

Resource inputs did not affect community ANPP in May and June, while N and/or NW enhanced ANPP in July and August. Resource inputs generally did not affect species richness, asynchrony or community stability in most of the time. Positive responses of perennial bunchgrasses (PB) to N and/or NW treatments contributed to the increased community ANPP in July and August. Species asynchrony may be the major mechanism contributing to community stability in May and June and the entire growing season, and PB stability is potentially the primary factor controlling community stability in July and August under resource enrichment. Our results indicate that season and resource availability could interact to regulate species richness, community ANPP and stability in semi-arid grasslands. These findings have important implications for management practices in semi-arid grasslands in order to mitigate the impact of land use and global change.

As the determinant of water availability in drylands, groundwater plays a fundamental role in regulating vegetation distribution and ecosystem processes. Although considerable progress has been made over the past years in the relationship between environment stress and plant community-level traits, the potential influence of water stress induced by groundwater changes on plant community-level stoichiometry remains largely unclear. Here, we examined whether belowground and aboveground community-level stoichiometry responded differently to groundwater changes.

We measured nitrogen (N) and phosphorus (P) concentrations in plant leaves and fine-roots of 110 plots under a broad range of groundwater depths in a typical arid inland river basin. We examined the spatial patterns and drivers of community-level N:P stoichiometry in leaves and fine-roots.

Community-level leaf and fine-root N, P and N:P ratios were mainly determined by groundwater, vegetation types and species composition, among which groundwater played a dominant role. Groundwater indirectly regulated community-level N:P stoichiometry through affecting vegetation types and species composition. Vegetation types and species composition had significant direct influences on community-level N:P stoichiometry. Furthermore, groundwater depth had opposite influences on community-level leaf and fine-root N:P stoichiometry. Groundwater depth regulated vegetation types and further decreased leaf N, P but increased leaf N:P ratios and fine-root N. Groundwater depth had a positive indirect impact on fine-root P but a negative indirect impact on fine-root N:P ratios primarily by affecting species composition. Our findings indicate that groundwater rather than climate conditions effectively regulates community-level N:P stoichiometry, and below- and aboveground N:P stoichiometry has opposite responses to groundwater.

Species diversity–productivity relationships in natural ecosystems have been well documented in the literature. However, biotic and abiotic factors that determine their relationships are still poorly understood, especially under future climate change scenarios.

Randomized block factorial experiments were performed in three meadows along an elevational gradient on Yulong Mountain, China, where open-top chambers and urea fertilizer manipulations were used to simulate warming and nitrogen addition, respectively. Besides species diversity, we measured functional diversity based on five traits: plant height, specific leaf area and leaf carbon, nitrogen and phosphorus contents. Several abiotic factors relating to climate (air temperature and precipitation) and soil chemistry (pH, organic carbon concentration, total nitrogen concentration and phosphorus concentration) were also measured. Generalized linear mixed-effect models were used to investigate the responses of species diversity and productivity to elevation, warming, nitrogen addition and their interactions. The effects of biotic and abiotic factors on the direction and magnitude of their relationship were also assessed.

Species diversity decreased with increasing elevation and declined under warming at mid-elevation, while productivity decreased with increasing elevation. Functional richness, maximum air temperature, soil pH and their interactions showed strong but negative influences on the species diversity–productivity relationship; the relationship shifted from positive to neutral and then to slightly negative as these sources of variation increased. Our study highlights the negative effects of short-term warming on species diversity and emphasizes the importance of both biotic and abiotic drivers of species diversity–productivity relationships in mountain meadow communities.

Plant–soil feedback (PSF) is a key mechanism that can facilitate tree species coexistence and diversity. Substantial evidence suggests that species-specific soil-borne pathogens around adult trees limit the performance of home (conspecific) seedlings relative to foreign (heterospecific) seedlings. However, the underlying mechanism remains largely elusive.

Here, we conducted a reciprocal transplant pot experiment using seedlings and from two tree species, Pinus massoniana and Lithocarpus glaber that are dominant and coexist in a subtropical, evergreen, broad-leaf forest in Gutianshan, Zhejiang Province of eastern China. We examined how seedlings from the two tree species responded to soils originating from underneath their own versus the other tree species, using a full-factorial design. Additionally, we added a fungicide (benomyl) to half of the pots to evaluate the role of soil-borne fungi on seedling growth.

We found that the seedlings from L. glaber grew better in soils that were collected from beneath the canopy of P. massoniana, while seedling growth of P. massioniana was not affected by soil origin. The addition of fungicide benomyl resulted in a shift towards more positive PSF effects for L. glaber, indicating that L. glaber seedlings performed better in their own soils than in soils from P. massoniana in the absence of fungi. Our findings highlight the importance of soil-borne pathogenic and ectomycorrhizal fungi in driving PSF, and indicate that PSF may promote the coexistence of two subtropical tree species by reducing the performance of L. glaber in own soils.