Forests harbour large spatiotemporal heterogeneity in canopy structure. This variation drives the microclimate and light availability at the forest floor. So far, we do not know how light availability and sub-canopy temperature interactively mediate the impact of macroclimate warming on understorey communities. We therefore assessed the functional response of understorey plant communities to warming and light addition in a full factorial experiment installed in temperate deciduous forests across Europe along natural microclimate, light and macroclimate gradients. Furthermore, we related these functional responses to the species' life-history syndromes and thermal niches. We found no significant community responses to the warming treatment. The light treatment, however, had a stronger impact on communities, mainly due to responses by fast-colonizing generalists and not by slow-colonizing forest specialists. The forest structure strongly mediated the response to light addition and also had a clear impact on functional traits and total plant cover. The effects of short-term experimental warming were small and suggest a time-lag in the response of understorey species to climate change. Canopy disturbance, for instance due to drought, pests or logging, has a strong and immediate impact and particularly favours generalists in the understorey in structurally complex forests.This article is protected by copyright. All rights reserved.

Understanding the sensitivity of tundra vegetation to climate warming is critical to forecasting future biodiversity and vegetation feedbacks to climate. In situ warming experiments accelerate climate change on a small scale to forecast responses of local plant communities. Limitations of this approach include the apparent site-specificity of results and uncertainty about the power of short-term studies to anticipate longer term change. We address these issues with a synthesis of 61 experimental warming studies, of up to 20 years duration, in tundra sites worldwide. The response of plant groups to warming often differed with ambient summer temperature, soil moisture and experimental duration. Shrubs increased with warming only where ambient temperature was high, whereas graminoids increased primarily in the coldest study sites. Linear increases in effect size over time were frequently observed. There was little indication of saturating or accelerating effects, as would be predicted if negative or positive vegetation feedbacks were common. These results indicate that tundra vegetation exhibits strong regional variation in response to warming, and that in vulnerable regions, cumulative effects of long-term warming on tundra vegetation - and associated ecosystem consequences - have the potential to be much greater than we have observed to date.© 2011 Blackwell Publishing Ltd/CNRS.

The relationship between the structure and function of forest ecosystems is the main intere-sts in the research area of forest ecology and management. However, over complex terrains in particular, these studies had been challenged as uneasy tasks due to the limitations in the forest survey and measurement techniques and other supporting technologies. Chinese Academy of Sciences (CAS) funded “Multi-Tower LiDAR/ECFlux Platform for Monitoring the Structure and Function of Secondary Forest Ecosystems” (Multi-Tower Platform, MTP) as a field station network corner-stone research infrastructure project, which was completed by Qingyuan Forest CERN (Chinese Ecosystem Research Network). In a distinctively-bounded and monitored-outlet watershed, the MTP was integrated by light detection and ranging (LiDAR) scanners, eddy covariance (EC) flux instrument systems, whole- and sub-watershed hydrology station network, long-term forest plot arrays, and live data center. Using LiDAR scanning, the MTP can get cloud data for holographic information on canopy structure. The EC-flux instrument system and hydrology station network along with forest plot arrays could ensure the reliability of water and carbon observations over this complex terrain, which allows to verify the studies on flux measurement technologies and methods, as well as to understand the processes of ecohydrology and CO₂ exchange between forest ecosystem and the atmosphere. Further, we can also assess the primary ecosystem services, including water conservation and carbon sequestration. All the data from “tower-station” were streamed through wireless network, which would facilitate data monitoring, management, and sharing. There are three tasks of MTP team: 1) defining innovative methods and descriptors to quantify three-dimensional forest structure; 2) developing theories and techniques to measure CO₂/H₂O fluxes and other trace gases over complex terrains; 3) understanding the relationship between structure and function of forest ecosystems, providing information and rationales for forest management practices to assure broad and sustainable benefits from forests.

森林生态系统结构与生态服务功能关系是森林生态学和林学的永恒研究主题。受传统森林调查方法及技术手段的限制,对复杂地形下森林生态系统结构和功能的监测及二者关系的研究面临诸多挑战。在中国科学院野外站网络重点科技基础设施建设项目的支持下,中国科学院清原森林生态系统观测研究站在独立流域内建成了以观测塔群(三座观测塔覆盖各自子流域代表性森林类型)为主体,集激光雷达(LiDAR)、通量仪器、水文站网、固定标准地和数据中心为综合体的“次生林生态系统塔群激光雷达监测平台”(简称塔群平台)。塔群平台采用激光雷达扫描获取森林点云数据,描述森林生态系统的全息三维结构;依托独立流域/子流域内的通量监测系统、水文监测站网和通量源区内的长期固定标准地,可保证碳-水过程观测的可靠性,并用于验证复杂地形下的通量监测技术与方法,揭示森林生态水文与碳交换过程,准确估算森林生态系统主体生态服务功能(水源涵养和固碳)。所有“塔-站”数据通过无线网络实时汇集于数据中心,便于数据监视、管理与共享。此外,塔群平台将侧重研究森林生态系统结构量化的新方法和新指标,探索复杂地形森林生态系统中H₂O/CO₂/痕量气体通量观测的理论与方法,为阐明森林结构与功能的关系、服务于森林生态系统管理提供基础数据。

青藏高原是全球变化的敏感区域，过去几十年以来，在全球气候变暖的背景下，藏北高原增温明显。本研究在藏北典型高寒草甸区采用开顶式生长室(OTC)模拟增温的方法，根据OTC的不同高度设置了4个增温梯度(40、60、80和100 cm)，分析了植物群落的生长、结构和组成以及生物量对增温的响应。结果表明：不同高度的OTC作用使得年平均空气温度增加了1.13～2.72 ℃，且OTC的高度越高，其增温效果越明显；伴随着温度的升高，空气湿度以及土壤湿度均有所降低；高山嵩草在所有群落中占有绝对优势，梯度增温作用使得其重要值不断下降；随着温度的升高，莎草类植物的盖度逐渐下降；对整个群落而言，增温幅度较低时，增温对群落的生长和生物量的积累以及多样性都会有明显的促进作用，当温度升高超过一定值，这种促进作用会逐渐减弱甚至变成抑制作用。本研究表明，藏北高寒草甸对增温作用具有敏感而迅速的响应，温度升高使该地区的气候朝着暖干化趋势发展，而一定程度的升温会促进植物群落的生长，但温度升高超过一定幅度时，会导致草地生产力下降，草地退化加剧。

Temperate forests cover 16% of the global forest area. Within these forests, the understorey is an important biodiversity reservoir that can influence ecosystem processes and functions in multiple ways. However, we still lack a thorough understanding of the relative importance of the understorey for temperate forest functioning. As a result, understoreys are often ignored during assessments of forest functioning and changes thereof under global change. We here compiled studies that quantify the relative importance of the understorey for temperate forest functioning, focussing on litter production, nutrient cycling, evapotranspiration, tree regeneration, pollination and pathogen dynamics. We describe the mechanisms driving understorey functioning and develop a conceptual framework synthesizing possible effects of multiple global change drivers on understorey-mediated forest ecosystem functioning. Our review illustrates that the understorey's contribution to temperate forest functioning is significant but varies depending on the ecosystem function and the environmental context, and more importantly, the characteristics of the overstorey. To predict changes in understorey functioning and its relative importance for temperate forest functioning under global change, we argue that a simultaneous investigation of both overstorey and understorey functional responses to global change will be crucial. Our review shows that such studies are still very scarce, only available for a limited set of ecosystem functions and limited to quantification, providing little data to forecast functional responses to global change.© 2019 John Wiley & Sons Ltd.

本研究以青藏高原高寒草甸为试验对象，利用开顶室增温装置（Open-Top-Chambers，OTCs），探讨4种增温幅度对物种多样性和生物量的影响。结果表明：群落盖度在高度增温下显著减少（PPPP<0.05），0~10 cm处地下生物量在高度增温下下减幅最大，20~30 cm处地下生物量在低度增温下增幅最大。本研究表明，在研究周期内物种丰富度对梯度增温响应不敏感，高度增温减少地上生物量的积累，地下生物量在不同幅度的增温处理下没有显著的变化规律性，响应并不敏感。

Plant phenology, the annually recurring sequence of plant developmental stages, is important for plant functioning and ecosystem services and their biophysical and biogeochemical feedbacks to the climate system. Plant phenology depends on temperature, and the current rapid climate change has revived interest in understanding and modeling the responses of plant phenology to the warming trend and the consequences thereof for ecosystems. Here, we review recent progresses in plant phenology and its interactions with climate change. Focusing on the start (leaf unfolding) and end (leaf coloring) of plant growing seasons, we show that the recent rapid expansion in ground- and remote sensing- based phenology data acquisition has been highly beneficial and has supported major advances in plant phenology research. Studies using multiple data sources and methods generally agree on the trends of advanced leaf unfolding and delayed leaf coloring due to climate change, yet these trends appear to have decelerated or even reversed in recent years. Our understanding of the mechanisms underlying the plant phenology responses to climate warming is still limited. The interactions between multiple drivers complicate the modeling and prediction of plant phenology changes. Furthermore, changes in plant phenology have important implications for ecosystem carbon cycles and ecosystem feedbacks to climate, yet the quantification of such impacts remains challenging. We suggest that future studies should primarily focus on using new observation tools to improve the understanding of tropical plant phenology, on improving process-based phenology modeling, and on the scaling of phenology from species to landscape-level.© 2019 John Wiley & Sons Ltd.

Earlier spring phenological events have been widely reported in plants under global warming. Recent studies reported a slowdown in the warming-induced advanced spring phenology in temperate regions. However, previous research mainly focused on daily mean temperature, thus neglecting the asymmetric phenological responses to daytime and nighttime temperature. Using long-term records of leaf unfolding in eight deciduous species at 1300 sites across central Europe, we assessed and compared the effects of daytime temperature, nighttime temperature, and photoperiod on leaf unfolding during 1951-1980 and 1981-2013. Although leaf unfolding was advanced by daytime warming during 1951-2013, the advancing responses of leaf unfolding significantly decreased from 1951-1980 to 1981-2013 due to a lower accumulation of chilling units by daytime warming. Nighttime warming delayed leaf unfolding during 1951-1980 but advanced it during 1981-2013 due to a higher accumulation of chilling units by nighttime warming. In contrast, critical daylength and plasticity of leaf unfolding dates remained unchanged between 1951 and 2013. Our study provided evidence that daytime warming instead of nighttime warming accounts for the slowdown in the advancing spring phenology and implied that nighttime warming-induced earlier spring phenology may be buffering the slowdown of the advanced spring phenology by daytime warming. The response of spring phenology to nighttime temperature may override that to daytime temperature under the actual trends in global warming.© 2021 John Wiley & Sons Ltd.

Experimental warming in situ suggests that warming could lead to a loss of biodiversity. However, species that remain in situ and experience climate change will interact with species tracking climate change, which could also affect patterns of biodiversity. The relative contribution of species gains and losses to net changes in species richness is still unclear. We use transplanted plant communities to test the hypothesis that both the change in climate and ecological communities tracking climate change will influence how species richness responds to climate change. Three intact alpine plant communities were reciprocally transplanted to create scenarios in which species experienced warmer and wetter conditions (transferred to lower elevations) and cooler and drier conditions (transferred to higher elevations) over 10 years on the Tibetan Plateau. Communities transplanted into the same elevation as controls represent species tracking climate change. Transferring to lower elevations generally caused a net increase in richness and a higher rate of gains relative to the control plots; the magnitude of this effect depended on the specific elevation. Transferring to higher elevations lead to either net increases or decreases in richness and gains, depending on elevation. Species gains predicted much more variation in changes in species richness (50%) than did species loss (9%). Species richness at the receptor site and the donor site were both important predictors of variation in species richness, and the abiotic environment did not explain additional variation. Changes in cover of dominant plant species in response to transfers did not predict changes in species richness, species gain or species loss. Our results suggest that species gains from species tracking climate change at the receptor sites, rather than species loss from the donor sites, predicted changes in species richness. Synthesis. Warming experiments with physical barriers to dispersal may overestimate the negative effect of warming on plant diversity by not accounting for species gains. Our study highlights the importance of biotic factors in addition to the abiotic environment, when considering how climate change will affect plant diversity.

Long-term monitoring, space-for-time substitutions along gradients, and in situ temperature manipulations are common approaches to understand effects of climate change on alpine and arctic plant communities. Although general patterns emerge from studies using different approaches, there are also some inconsistencies. To provide better estimates of plant community responses to future warming across a range of environments, there have been repeated calls for integrating different approaches within single studies. Thus, to examine how different methods in climate change effect studies may ask different questions, we combined three climate warming approaches in a single study in the Hengduan Mountains of southwestern China. We monitored plant communities along an elevation gradient using the space-for-time approach, and conducted warming experiments using open top chambers (OTCs) and plant community transplantation toward warmer climates along the same gradient. Plant species richness and abundances were monitored over 5 years addressing two questions: (1) how do plant communities respond to the different climate warming approaches? (2) how can the combined approaches improve predictions of plant community responses to climate change? The general trend across all three approaches was decreased species richness with climate warming at low elevations. This suggests increased competition from immigrating lowland species, and/or from the species already growing inside the plots, as indicated by increased biomass, vegetation height or proportion of graminoids. At the coldest sites, species richness decreased in OTCs and along the gradient, but increased in the transplants, suggesting that plant communities in colder climates are more open to invasion from lowland species, with slow species loss. This was only detected in the transplants, showing that different approaches, may yield different results. Whereas OTCs may constrain immigration of new species, transplanted communities are rapidly exposed to new neighbors that can easily colonize the small plots. Thus, different approaches ask slightly different questions, in particular regarding indirect climate change effects, such as biotic interactions. To better understand both direct and indirect effects of climate change on plant communities, we need to combine approaches in future studies, and if novel interactions are of particular interest, transplants may be a better approach than OTCs.

Global climate warming and increasing nitrogen (N) deposition, as controversial global environmental issues, may distinctly affect the functions and processes of terrestrial ecosystems. It has been reported that the Qinghai-Tibet Plateau has been experiencing significant warming in recent decades, especially in winter. Previous studies have mainly focused on the effects of warming all the year round; however, few studies have tested the effects of winter warming. To investigate the effects of winter warming and N addition on plant community structure and species composition of alpine meadow, long-term N addition and simulated warming experiment was conducted in alpine meadow from 2010 in Damxung, northern Tibet. The experiment consisted of three warming patterns: Year-round warming (YW), winter warming (WW) and control (NW), crossed respectively with five N gradients: 0, 10, 20, 40, 80 kg N·hm^-2·a^-1. From 2012 to 2014, both warming and N addition significantly affected the total coverage of plant community. Specifically, YW significantly decreased the total coverage of plant community. Without N addition, WW remarkably reduced the vegetation coverage. However, with N addition, the total vegetation coverage gradually increased with the increase of N level. Warming and N addition had different effects on plants from different functional groups. Warming significantly reduced the plant coverage of grasses and sedges, while N addition significantly enhanced the plant coverage of grasses. Regression analyses showed that the total coverage of plant community was positively related to soil water content in vigorous growth stages, indicating that the decrease in soil water content resulted from warming during dry seasons might be the main reason for the decline of total community coverage. As soil moisture in semi-arid alpine meadow is mainly regulated by rainfalls, our results indicated that changes in spatial and temporal patterns of rainfalls under the future climate change scenarios would dramatically influence the vegetation coverage and species composition. Additionally, the effects of increasing atmospheric N deposition on vegetation community might also depend on the change of rainfall patterns.

气候变暖和氮沉降增加作为全球环境问题,将严重影响陆地生态系统的结构与功能.研究发现,近几十年来青藏高原增温显著,其中冬季升温最明显.而已有的研究更多关注全年增温,对冬季增温研究较少.本文基于高寒草甸地区增温和氮素添加影响研究的不足,在青藏高原高寒草甸区开展模拟增温和氮添加试验,研究长期增温与氮添加对高寒草甸群落结构与物种组成的影响.试验布设于2010年7月,地点在西藏当雄高寒草甸区,共有3种增温方式:对照、全年增温、冬季增温;每种增温处理下设置5个氮素添加梯度:0、10、20、40、80 kg N·hm^-2·a^-1,系统研究气候变暖与氮添加对高寒草甸生态系统群落结构与物种组成的影响.结果表明: 2012—2014年,增温与施氮处理均显著影响群落总盖度:全年增温处理降低了群落总盖度;在不施氮处理下,冬季增温降低了群落盖度,但在施氮处理下,随着氮剂量的提高群落盖度逐渐升高.增温与施氮对不同功能群植物的影响不同,增温处理降低了禾草与莎草植物盖度,而施氮提高了禾草植物盖度.相关分析表明,植被群落总盖度与生长旺盛期土壤含水量呈正相关关系,推测在降雨较少的季节增温导致的土壤含水量降低是群落盖度降低的主要原因.半干旱区高寒草甸土壤水分主要受降雨的调控,未来气候变化情景下,降雨时空格局的改变会显著影响植被群落盖度及组成,且大气氮沉降的增加对植被群落的影响也依赖于降雨条件的变化.