Changes in biocrust cover drive carbon cycle responses to climate change in drylands

Dryland ecosystems account for ca. 27% of global soil organic carbon (C) reserves, yet it is largely unknown how climate change will impact C cycling and storage in these areas. In drylands, soil C concentrates at the surface, making it particularly sensitive to the activity of organisms inhabiting the soil uppermost levels, such as communities dominated by lichens, mosses, bacteria and fungi (biocrusts). We conducted a full factorial warming and rainfall exclusion experiment at two semiarid sites in Spain to show how an average increase of air temperature of 2–3 °C promoted a drastic reduction in biocrust cover (ca. 44% in 4 years). Warming significantly increased soil CO₂ efflux, and reduced soil net CO₂ uptake, in biocrust‐dominated microsites. Losses of biocrust cover with warming through time were paralleled by increases in recalcitrant C sources, such as aromatic compounds, and in the abundance of fungi relative to bacteria. The dramatic reduction in biocrust cover with warming will lessen the capacity of drylands to sequester atmospheric CO₂. This decrease may act synergistically with other warming‐induced effects, such as the increase in soil CO₂ efflux and the changes in microbial communities to alter C cycling in drylands, and to reduce soil C stocks in the mid to long term.     

黄土高原藓结皮土壤呼吸速率对降雨量变化的响应

全球气候变化加剧背景下,干旱和半干旱地区的降雨模式将进一步改变,其造成的土壤水分波动是引起土壤呼吸动态变化的重要因素,但生物结皮土壤呼吸响应降雨模式变化继而影响陆地生态系统碳源/汇功能的机制尚不明确。针对黄土高原风沙土发育的藓结皮,以自然降雨量为对照,分别进行幅度为10%、30%、50%的模拟增雨和减雨处理,并利用便携式土壤碳通量分析仪(LI-8100A)测定了模拟增减雨后的藓结皮土壤呼吸速率,对比分析了其对降雨量变化的响应及机制。结果表明：(1)整个实验周期(2018和2019)增雨和减雨分别显著提高(增幅分别为17.9%—48.2%和27.1%—54.2%)和降低了(降幅分别为1.8%—26.8%和5.2%—20.8%)土壤含水量,但对土壤温度的影响不显著;(2)增雨抑制了藓结皮土壤呼吸速率(降幅分别为7.8%—31.7%和14.7%—39.4%),且随梯度增大抑制作用越明显;减雨则取决于减雨梯度,减雨10%和30%会促进土壤呼吸速率(增幅分别为27.5%、9.6%和23.6%、9.7%)而减雨50%具有抑制作用(降幅分别为15.6%和18.5%)。不同实验周期和不同降雨处理间藓结...     

Microsite enhancements for soil stabilization and rapid biocrust colonization in degraded drylands

In dryland ecosystems, natural recovery of biological soil crusts (biocrusts) following disturbance may be slow or inhibited, necessitating active restoration practices. While biocrusts can be readily propagated under environmentally controlled conditions, rehabilitation in the field is complicated by environmental stresses which may be particularly acute in degraded, destabilized soils with harsh climatic conditions at the soil surface. In this study, we first present the results of a field trial at a severely degraded rangeland site examining the stabilizing effects of various soil amendments (polysaccharide glues and polyacrylamides) in combination with biocrust inoculum. We found that a psyllium compound was the only amendment to maintain effectiveness after 19 months, and the only treatment that maintained biocrust inoculum throughout the trial. In a subsequent short‐term experiment where plots were shaded and watered, we examined how biocrust inoculation rate (0, 20, and 40% initial cover) and the psyllium‐based amendment affected biocrust growth. After 4 months, visible biocrust cover in inoculated plots was greater than in controls, but only chlorophyll a exhibited a dosage‐response to inoculum application rate, indicating preferential establishment of cyanobacteria. Psyllium did not affect biocrust development but did improve soil stability. Shade and watering buffered against temperature extremes (up to 15°C) and increased the duration of moist surface conditions necessary for biocrust growth by up to 30%, mimicking conditions more common in the fall and winter months. Our results suggest that inducing early successional biocrusts on a highly degraded site is possible with suitable microclimate conditions.     

Pathways regulating decreased soil respiration with warming in a biocrust‐dominated dryland

A positive soil carbon (C)‐climate feedback is embedded into the climatic models of the IPCC. However, recent global syntheses indicate that the temperature sensitivity of soil respiration (R_S) in drylands, the largest biome on Earth, is actually lower in warmed than in control plots. Consequently, soil C losses with future warming are expected to be low compared with other biomes. Nevertheless, the empirical basis for these global extrapolations is still poor in drylands, due to the low number of field experiments testing the pathways behind the long‐term responses of soil respiration (R_S) to warming. Importantly, global drylands are covered with biocrusts (communities formed by bryophytes, lichens, cyanobacteria, fungi, and bacteria), and thus, R_S responses to warming may be driven by both autotrophic and heterotrophic pathways. Here, we evaluated the effects of 8‐year experimental warming on R_S, and the different pathways involved, in a biocrust‐dominated dryland in southern Spain. We also assessed the overall impacts on soil organic C (SOC) accumulation over time. Across the years and biocrust cover levels, warming reduced R_S by 0.30 μmol CO₂ m^?2 s^?1 (95% CI = ?0.24 to 0.84), although the negative warming effects were only significant after 3 years of elevated temperatures in areas with low initial biocrust cover. We found support for different pathways regulating the warming‐induced reduction in R_S at areas with low (microbial thermal acclimation via reduced soil mass‐specific respiration and β‐glucosidase enzymatic activity) vs. high (microbial thermal acclimation jointly with a reduction in autotrophic respiration from decreased lichen cover) initial biocrust cover. Our 8‐year experimental study shows a reduction in soil respiration with warming and highlights that biocrusts should be explicitly included in modeling efforts aimed to quantify the soil C–climate feedback in drylands.     

Production of greenhouse‐grown biocrust mosses and associated cyanobacteria to rehabilitate dryland soil function

Mosses are an often‐overlooked component of dryland ecosystems, yet they are common members of biological soil crust communities (biocrusts) and provide key ecosystem services, including soil stabilization, water retention, carbon fixation, and housing of N₂ fixing cyanobacteria. Mosses are able to survive long dry periods, respond rapidly to precipitation, and reproduce vegetatively. With these qualities, dryland mosses have the potential to be an excellent dryland restoration material. Unfortunately, dryland mosses are often slow growing in nature, and ex situ cultivation methods are needed to enhance their utility. Our goal was to determine how to rapidly produce, vegetatively, Syntrichia caninervis and S. ruralis, common and abundant moss species in drylands of North America and elsewhere, in a greenhouse. We manipulated the length of hydration on a weekly schedule (5, 4, 3, or 2 days continuous hydration per week), crossed with fertilization (once at the beginning, monthly, biweekly, or not at all). Moss biomass increased sixfold for both species in 4 months, an increase that would require years under dryland field conditions. Both moss species preferred short hydration and monthly fertilizer. Remarkably, we also unintentionally cultured a variety of other important biocrust organisms, including cyanobacteria and lichens. In only 6 months, we produced functionally mature biocrusts, as evidenced by high productivity and ecosystem‐relevant levels of N₂ fixation. Our results suggest that biocrust mosses might be the ideal candidate for biocrust cultivation for restoration purposes. With optimization, these methods are the first step in developing a moss‐based biocrust rehabilitation technology.     

Photosynthesis and growth reduction with warming are driven by nonstomatal limitations in a Mediterranean semi‐arid shrub

Whereas warming enhances plant nutrient status and photosynthesis in most terrestrial ecosystems, dryland vegetation is vulnerable to the likely increases in evapotranspiration and reductions in soil moisture caused by elevated temperatures. Any warming‐induced declines in plant primary production and cover in drylands would increase erosion, land degradation, and desertification. We conducted a four‐year manipulative experiment in a semi‐arid Mediterranean ecosystem to evaluate the impacts of a ~2°C warming on the photosynthesis, transpiration, leaf nutrient status, chlorophyll content, isotopic composition, biomass growth, and postsummer survival of the native shrub Helianthemum squamatum. We predicted that warmed plants would show reduced photosynthetic activity and growth, primarily due to the greater stomatal limitation imposed by faster and more severe soil drying under warming. On average, warming reduced net photosynthetic rates by 36% across the study period. Despite this strong response, warming did not affect stomatal conductance and transpiration. The reduction of peak photosynthetic rates with warming was more pronounced in a drought year than in years with near‐average rainfall (75% and 25–40% reductions relative to controls, respectively), with no indications of photosynthetic acclimation to warming through time. Warmed plants had lower leaf N and P contents, δ¹³C, and sparser and smaller leaves than control plants. Warming reduced shoot dry mass production by 31%. However, warmed plants were able to cope with large reductions in net photosynthesis, leaf area, and shoot biomass production without changes in postsummer survival rates. Our findings highlight the key role of nonstomatal factors (biochemical and/or nutritional) in reducing net carbon assimilation rates and growth under warming, which has important implications for projections of plant carbon balance under the warmer and drier climatic scenario predicted for drylands worldwide. Projected climate warming over the coming decades could reduce net primary production by about one‐third in semi‐arid gypsum shrublands dominated by H. squamatum.     

Addressing barriers to improve biocrust colonization and establishment in dryland restoration

Methods to reduce soil loss and associated loss of ecosystem functions due to land degradation are of particular importance in dryland ecosystems. Biocrusts are communities of cyanobacteria, lichens, and bryophytes that are vulnerable to soil disturbance, but provide vital ecosystem functions when present. Biocrusts stabilize soil, improve hydrologic function, and increase nutrient and carbon inputs. Methods to reestablish biocrust rapidly, when lost from ecosystems, have the potential to restore important dryland ecosystem functions and thereby increase probability of successful rehabilitation. The aim of this study was to identify habitat ameliorations to enhance the success of biocrust inoculation by: (1) reducing physiological stress on biocrusts and increasing resource availability (using shade, soil surface roughening, and watering), and (2) stabilizing mobile soils (using straw borders, three soil tackifiers [soil stabilizers], and a combination of shade, water, roughening, and tackifier). In the Great Basin Desert on the Utah Test and Training Range near Salt Lake City, we applied field‐harvested biocrust material to experimental plots on coarse‐ and fine‐textured soils with the top 2 cm of soil and biocrust removed. Habitat ameliorations were applied with and without biocrust addition. Shade provision increased biocrust cover 50% over controls. Biocrust cover and soil stability were 65% lower in straw border plots relative to controls. Soil tackifiers, alone and in combination with resource augmentation and stress reduction, did not improve cover and stabilization over inoculated controls. We found variability in recovery by time and between soil types. These results suggest plausible strategies to improve success of biocrust inoculation.     

Biological soil crusts in ecological restoration: emerging research and perspectives

Drylands encompass over 40% of terrestrial ecosystems and face significant anthropogenic degradation causing a loss of ecosystem integrity, services, and deterioration of social‐ecological systems. To combat this degradation, some dryland restoration efforts have focused on the use of biological soil crusts (biocrusts): complex communities of cyanobacteria, algae, lichens, bryophytes, and other organisms living in association with the top millimeters of soil. Biocrusts are common in many ecosystems and especially drylands. They perform a suite of ecosystem functions: stabilizing soil surfaces to prevent erosion, contributing carbon through photosynthesis, fixing nitrogen, and mediating the hydrological cycle in drylands. Biocrusts have emerged as a potential tool in restoration; developing methods to implement effective biocrust restoration has the potential to return many ecosystem functions and services. Although culture‐based approaches have allowed researchers to learn about the biology, physiology, and cultivation of biocrusts, transferring this knowledge to field implementation has been more challenging. A large amount of research has amassed to improve our understanding of biocrust restoration, leaving us at an opportune time to learn from one another and to join approaches for maximum efficacy. The articles in this special issue improve the state of our current knowledge in biocrust restoration, highlighting efforts to effectively restore biocrusts through a variety of different ecosystems, across scales and utilizing a variety of lab and field methods. This collective work provides a useful resource for the scientific community as well as land managers.     

Strategies for restoring the structure and function of lichen‐moss biocrust communities

Biological soil crusts (biocrusts) are crucial components of dryland ecosystems, but they are slow to recover following disturbance. Herein, we evaluated several methods for restoring lichen‐moss biocrusts that included factorial applications of moss fragments in a water‐slurry (1) with and without lichen fragments (to restore biocrust taxonomic structure), (2) with and without clay (to facilitate establishment), and (3) with and without jute ground cloth (to facilitate establishment). Three and four years after inoculation, moss and lichen cover was up to five and eight times higher on jute ground cloth than on bare ground, respectively. Lichen cover was six times higher in plots where lichen fragments were added. Clay amendments did not increase moss or lichen establishment. To understand the effects of biocrust recovery on soil properties, we measured soil inorganic nitrogen, microbial biomass carbon, and soil water availability in restoration and control plots. Restored biocrusts decreased inorganic NH₄‐N availability by 67% when compared to controls 3 years after inoculation, but did not influence the availability of inorganic NO₃‐N, soil water, or microbial biomass carbon. Our results demonstrate that adding a biocrust inoculant to jute ground cloth can expedite recovery of lichen‐moss biocrust and reestablish its influence on soil properties within a few years.     

Increased temperature and altered summer precipitation have differential effects on biological soil crusts in a dryland ecosystem

Biological soil crusts (biocrusts) are common and ecologically important members of dryland ecosystems worldwide, where they stabilize soil surfaces and contribute newly fixed C and N to soils. To test the impacts of predicted climate change scenarios on biocrusts in a dryland ecosystem, the effects of a 2–3 °C increase in soil temperature and an increased frequency of smaller summer precipitation events were examined in a large, replicated field study conducted in the cold desert of the Colorado Plateau, USA. Surface soil biomass (DNA concentration), photosynthetically active cyanobacterial biomass (chlorophyll a concentration), cyanobacterial abundance (quantitative PCR assay), and bacterial community composition (16S rRNA gene sequencing) were monitored seasonally over 2 years. Soil microbial biomass and bacterial community composition were highly stratified between the 0–2 cm depth biocrusts and 5–10 cm depth soil beneath the biocrusts. The increase in temperature did not have a detectable effect on any of the measured parameters over 2 years. However, after the second summer of altered summer precipitation pattern, significant declines occurred in the surface soil biomass (avg. DNA concentration declined 38%), photosynthetic cyanobacterial biomass (avg. chlorophyll a concentration declined 78%), cyanobacterial abundance (avg. gene copies g^?1 soil declined 95%), and proportion of Cyanobacteria in the biocrust bacterial community (avg. representation in sequence libraries declined 85%). Biocrusts are important contributors to soil stability, soil C and N stores, and plant performance, and the loss or reduction of biocrusts under an altered precipitation pattern associated with climate change could contribute significantly to lower soil fertility and increased erosion and dust production in dryland ecosystems at a regional scale.     

Biological soil crust salvage for dryland restoration: an opportunity for natural resource restoration

Biocrusts' functional importance and vulnerability to disturbance have motivated consistent interest in biocrust restoration, as well as a recent increase in research to cultivate biocrusts in laboratory and greenhouse settings for use in ecological restoration. As part of a sustainable approach to developing biocrust restoration, we argue that a complementary step is to improve and accelerate methods for salvaging biocrusts that would otherwise be destroyed in a forthcoming disturbance. The increasing rate and scale of disturbance pressures in drylands where biocrusts flourish means that the supply of salvageable biocrust and demand for that material in restoration greatly exceed the present cultivable supply. In this article we describe the state of knowledge for biocrust salvage, present a simple set of steps for conducting a salvage harvest, discuss risks and benefits when considering using salvage, and suggest future research directions to facilitate scaling up biocrust restoration using salvaged material. A focus on the use of salvaged biocrust as a restoration source may prove an important step to improve ecological restoration in notoriously difficult to restore dryland ecosystems.     

Climate Change and Physical Disturbance Manipulations Result in Distinct Biological Soil Crust Communities

Biological soil crusts (biocrusts) colonize plant interspaces in many drylands and are critical to soil nutrient cycling. Multiple climate change and land use factors have been shown to detrimentally impact biocrusts on a macroscopic (i.e., visual) scale. However, the impact of these perturbations on the bacterial components of the biocrusts remains poorly understood. We employed multiple long-term field experiments to assess the impacts of chronic physical (foot trampling) and climatic changes (2°C soil warming, altered summer precipitation [wetting], and combined warming and wetting) on biocrust bacterial biomass, composition, and metabolic profile. The biocrust bacterial communities adopted distinct states based on the mechanism of disturbance. Chronic trampling decreased biomass and caused small community compositional changes. Soil warming had little effect on biocrust biomass or composition, while wetting resulted in an increase in the cyanobacterial biomass and altered bacterial composition. Warming combined with wetting dramatically altered bacterial composition and decreased Cyanobacteria abundance. Shotgun metagenomic sequencing identified four functional gene categories that differed in relative abundance among the manipulations, suggesting that climate and land use changes affected soil bacterial functional potential. This study illustrates that different types of biocrust disturbance damage biocrusts in macroscopically similar ways, but they differentially impact the resident soil bacterial communities, and the communities'' functional profiles can differ depending on the disturbance type. Therefore, the nature of the perturbation and the microbial response are important considerations for management and restoration of drylands.     

Decade of experimental permafrost thaw reduces turnover of young carbon and increases losses of old carbon,without affecting the net carbon balance

Thicker snowpacks and their insulation effects cause winter‐warming and invoke thaw of permafrost ecosystems. Temperature‐dependent decomposition of previously frozen carbon (C) is currently considered one of the strongest feedbacks between the Arctic and the climate system, but the direction and magnitude of the net C balance remains uncertain. This is because winter effects are rarely integrated with C fluxes during the snow‐free season and because predicting the net C balance from both surface processes and thawing deep layers remains challenging. In this study, we quantified changes in the long‐term net C balance (net ecosystem production) in a subarctic peat plateau subjected to 10 years of experimental winter‐warming. By combining ²¹⁰Pb and ¹⁴Cdating of peat cores with peat growth models, we investigated thawing effects on year‐round primary production and C losses through respiration and leaching from both shallow and deep peat layers. Winter‐warming and permafrost thaw had no effect on the net C balance, but strongly affected gross C fluxes. Carbon losses through decomposition from the upper peat were reduced as thawing of permafrost induced surface subsidence and subsequent waterlogging. However, primary production was also reduced likely due to a strong decline in bryophytes cover while losses from the old C pool almost tripled, caused by the deepened active layer. Our findings highlight the need to estimate long‐term responses of whole‐year production and decomposition processes to thawing, both in shallow and deep soil layers, as they may contrast and lead to unexpected net effects on permafrost C storage.     

Plant recovery techniques do not ensure biological soil‐crust recovery after gypsum quarrying: a call for active restoration

Biological soil crusts (biocrusts) are a key component of dryland ecosystems worldwide. However, large extensions of biocrusts are disturbed by human activities, gypsum quarry being an outstanding example. Restoration techniques applied have offered satisfactory results for vascular plants but they could greatly differ in promoting biocrust recovery. A basic question remains unaddressed: can measures for plant recovery accelerate or promote the recovery of biological crusts? We have examined eight different situations: undisturbed natural habitat, five treatments with no restoration measures (overgrazed area, abandoned quarry, topsoil removal from natural habitat, and two areas filled with gypsum mining spoil), and 2 areas receiving restoration measures (manual sowing and hydroseeding). We took 40 soil cores to determine cover of lichen, moss, and cyanobacteria. Biocrust richness and cover were higher in the undisturbed habitat, with remarkable differences for the different components among treatments. Cyanobacteria were well represented in all the cores (restored and non‐restored). Mosses were promoted the most by hydroseeding. Lichen cover was remarkably higher in undisturbed samples, very low in the quarry abandoned in 1992, and 0 in the rest. Complete spontaneous recovery of biocrusts was inefficient in the 25‐year period examined. Plant restoration measures could speed up its recovery comparing with non‐restored areas. Cyanobacteria and mosses can spontaneously recover fairly well. However, promoting them would accelerate the appearance of lichen. For lichen, inoculation or translocation of lichen thalli might be proposed. Therefore, our results call for the inclusion of active restoration measures of biocrust components in recovery plans, especially for lichens.     

The pervasive and multifaceted influence of biocrusts on water in the world's drylands

The capture and use of water are critically important in drylands, which collectively constitute Earth's largest biome. Drylands will likely experience lower and more unreliable rainfall as climatic conditions change over the next century. Dryland soils support a rich community of microphytic organisms (biocrusts), which are critically important because they regulate the delivery and retention of water. Yet despite their hydrological significance, a global synthesis of their effects on hydrology is lacking. We synthesized 2,997 observations from 109 publications to explore how biocrusts affected five hydrological processes (times to ponding and runoff, early [sorptivity] and final [infiltration] stages of water flow into soil, and the rate or volume of runoff) and two hydrological outcomes (moisture storage, sediment production). We found that increasing biocrust cover reduced the time for water to pond on the surface (?40%) and commence runoff (?33%), and reduced infiltration (?34%) and sediment production (?68%). Greater biocrust cover had no significant effect on sorptivity or runoff rate/amount, but increased moisture storage (+14%). Infiltration declined most (?56%) at fine scales, and moisture storage was greatest (+36%) at large scales. Effects of biocrust type (cyanobacteria, lichen, moss, mixed), soil texture (sand, loam, clay), and climatic zone (arid, semiarid, dry subhumid) were nuanced. Our synthesis provides novel insights into the magnitude, processes, and contexts of biocrust effects in drylands. This information is critical to improve our capacity to manage dwindling dryland water supplies as Earth becomes hotter and drier.     

黄土丘陵区草本植物覆盖下生物结皮对坡面径流流速的削减作用

生物结皮是干旱半干旱地区的常见地被物,与植物共同影响坡面径流及流速。迄今鲜有研究关注植物和生物结皮共同覆盖对流速的影响,是干旱半干旱地区坡面侵蚀驱动因素研究的薄弱环节。本研究以黄土丘陵区退耕草地为对象,通过野外模拟降雨试验,研究草本植物覆盖下有无生物结皮及不同组成生物结皮(多藻少藓、多藓少藻和藓)对径流流速的影响。结果表明: 植物和植物+生物结皮覆盖显著降低了流速,植物覆盖较裸土降低70.7%,植物+生物结皮覆盖较裸土降低83.1%;植物和生物结皮共同覆盖下,植物和生物结皮对径流流速的削减效益分别为70.7%和12.4%。植物覆盖下生物结皮对流速的影响程度与其组成有关,多藻少藓结皮、多藓少藻结皮和藓结皮对流速的削减效益分别为11.5%、12.4%和19.4%。流速与藓盖度呈显著负相关,与藻盖度呈显著正相关,藓结皮盖度(x)与流速(y)的关系式为:y=-2.081x+0.03(R²=0.469)。当植物盖度一定时(40%±10%),生物结皮组成中藓盖度是影响共同覆盖坡面流速的关键因子。综上,草本植物覆盖下生物结皮有显著减缓流速的作用,且作用程度与其组成有关。表明在研究退耕草地坡面侵蚀动力机制时,生物结皮的作用应予以考虑。     

Increased high‐latitude photosynthetic carbon gain offset by respiration carbon loss during an anomalous warm winter to spring transition

Arctic and boreal ecosystems play an important role in the global carbon (C) budget, and whether they act as a future net C sink or source depends on climate and environmental change. Here, we used complementary in situ measurements, model simulations, and satellite observations to investigate the net carbon dioxide (CO₂) seasonal cycle and its climatic and environmental controls across Alaska and northwestern Canada during the anomalously warm winter to spring conditions of 2015 and 2016 (relative to 2010–2014). In the warm spring, we found that photosynthesis was enhanced more than respiration, leading to greater CO₂ uptake. However, photosynthetic enhancement from spring warming was partially offset by greater ecosystem respiration during the preceding anomalously warm winter, resulting in nearly neutral effects on the annual net CO₂ balance. Eddy covariance CO₂ flux measurements showed that air temperature has a primary influence on net CO₂ exchange in winter and spring, while soil moisture has a primary control on net CO₂ exchange in the fall. The net CO₂ exchange was generally more moisture limited in the boreal region than in the Arctic tundra. Our analysis indicates complex seasonal interactions of underlying C cycle processes in response to changing climate and hydrology that may not manifest in changes in net annual CO₂ exchange. Therefore, a better understanding of the seasonal response of C cycle processes may provide important insights for predicting future carbon–climate feedbacks and their consequences on atmospheric CO₂ dynamics in the northern high latitudes.     

Responses of terrestrial ecosystems to temperature and precipitation change: a meta‐analysis of experimental manipulation

Global mean temperature is predicted to increase by 2–7 °C and precipitation to change across the globe by the end of this century. To quantify climate effects on ecosystem processes, a number of climate change experiments have been established around the world in various ecosystems. Despite these efforts, general responses of terrestrial ecosystems to changes in temperature and precipitation, and especially to their combined effects, remain unclear. We used meta‐analysis to synthesize ecosystem‐level responses to warming, altered precipitation, and their combination. We focused on plant growth and ecosystem carbon (C) balance, including biomass, net primary production (NPP), respiration, net ecosystem exchange (NEE), and ecosystem photosynthesis, synthesizing results from 85 studies. We found that experimental warming and increased precipitation generally stimulated plant growth and ecosystem C fluxes, whereas decreased precipitation had the opposite effects. For example, warming significantly stimulated total NPP, increased ecosystem photosynthesis, and ecosystem respiration. Experimentally reduced precipitation suppressed aboveground NPP (ANPP) and NEE, whereas supplemental precipitation enhanced ANPP and NEE. Plant productivity and ecosystem C fluxes generally showed higher sensitivities to increased precipitation than to decreased precipitation. Interactive effects of warming and altered precipitation tended to be smaller than expected from additive, single‐factor effects, though low statistical power limits the strength of these conclusions. New experiments with combined temperature and precipitation manipulations are needed to conclusively determine the importance of temperature–precipitation interactions on the C balance of terrestrial ecosystems under future climate conditions.     

Global patterns of the responses of leaf-level photosynthesis and respiration in terrestrial plants to experimental warming

Aims The balance between leaf photosynthesis and respiration of terrestrial plants determines the net carbon (C) gain by vegetation and consequently is important to climate–C cycle feedback. This study is to reveal the global patterns of the responses of leaf-level net photosynthesis and dark respiration to elevated temperature.Methods Data for leaf-level net photosynthesis rate (P n) and dark respiration rate (R d) in natural terrestrial plant species with standard deviation (or standard error or confidence interval) and sample size were collected from searched literatures on Web of Science. Then a meta-analysis was conducted to estimate the effects of experimental warming on leaf-level P n and R d of terrestrial plants.Important findings Across all the plants included in the analysis, warming enhanced P n and R d significantly by 6.13 and 33.14%, respectively. However, the responses were plant functional type (PFT) specific. Specifically, photosynthesis of C₄ herbs responded to experimental warming positively but that of C₃ herbs did not, whereas their respiratory responses were similar, suggesting C₄ plants would benefit more from warming. The photosynthetic response declined linearly with increasing ambient temperature. The respiratory responses linearly enhanced with the increase in warming magnitude. In addition, a thermal acclimation of R d, instead of P n, was observed. Although greater proportion of fixed C was consumed (greater R d / P n ratio), warming significantly enhanced the daily net C balance at the leaf level. This provides an important mechanism for the positive responses of plant biomass and net primary productivity to warming. Overall, the findings, including the contrastive responses of different PFTs and the enhancement in daily leaf net C balance, are important for improving model projection of the climate–C cycle feedback.     

腾格里沙漠东南缘不同生物土壤结皮细菌多样性及其季节动态特征

微生物多样性对于生物土壤结皮在沙漠生态系统中改善局部环境以及提升生态功能具有重要作用。本研究对腾格里沙漠东南缘沙坡头地区藻结皮、藓结皮及其下层的四季样品进行了16S rDNA高通量测序, 以期阐明细菌多样性及其在生物土壤结皮演替过程中的季节变化规律。结果表明4种类型样品的细菌丰富度在夏季显著低于其他3个季节。4种类型样品中主要的细菌类群为变形菌门、放线菌门、绿弯菌门、酸杆菌门、蓝细菌门等, 其中变形菌门和放线菌门为优势类群, 夏季时变形菌门的相对多度显著高于春季、秋季、冬季, 且在结皮层中相对多度显著高于结皮下层。放线菌门的相对多度在春季、夏季显著高于秋季、冬季, 且结皮下层相对多度高于结皮层。生物土壤结皮演替过程中细菌多样性及其相对多度季节动态变化表明其对沙漠土壤局部环境的变化作出了响应, 这为深入理解生物土壤结皮在沙漠生态系统中的生态功能提供了微生物多样性数据。