Aboveground Net Primary Production Research Articles

Temporal changes in biomass production across different plant communities in alpine meadows of Tungnath, Garhwal Himalaya

We studied temporal changes in biomass and net primary productivity of alpine grasslands at Tungnath in Garhwal Himalaya. Five different communities with similar elevations were taken for investigation. The above-ground biomass samples were harvested as close to the ground as possible. Similarly, below-ground biomass samples were collected from harvesting monoliths (25 x 25 x 30 cm). Aboveground net primary production was determined as the sum of positive changes in biomass and belowground net primary production was calculated as the difference between peak belowground biomass and preceding minimum biomass. The live shoot biomass increased from May till September in all communities except Trachydium roylei and Polygonum, which peaked in August. The dead shoot and litter biomass first decreased and peaked in all communities in October. Belowground biomass first decreased and then increased towards the end of the growing season. The belowground to aboveground biomass ratio ranged between 0.61-3.08. The aboveground net productivity ranged between 454.8-294.3 g m-2, and the belowground net productivity ranged between 346.3-102.4 g m-2.

Overcompensation of ecosystem productivity following sustained extreme drought in a semiarid grassland.

Drought events are projected to be more extreme and frequent in the future and have profound influences on the structure and functions of terrestrial ecosystems. Thus, better understanding the mechanisms of recovery is critical for predicting the future dynamics of terrestrial ecosystems. We performed a 7-year field precipitation experiment to examine recovery of a grassland ecosystem from different magnitudes of sustained drought, from slight to extreme. The ecosystem was exposed to precipitation treatments in the first 3 years (2010-2012) and recovered during the last 4 years (2013-2016) without precipitation treatments. Overall, large reductions of aboveground net primary productivity (ANPP, -43.3%) and perennial forb biomass (-83.1%) were observed in the third year (2012) of extreme drought only. Nevertheless, ANPP fully recovered within 1 year after the drought treatments were terminated, and the rapid recovery was mainly due to increased soil total nitrogen and root biomass allocation after drought. Surprisingly, large increases of ANPP under the extreme drought treatment occurred during the recovery periods from 2013 to 2015 (+74.1, +88.5, and +119.8 g m-2 year-1 ) compared to the control. The overcompensation offset the extreme drought-induced reduction of ANPP in the treatment years and was primarily ascribed to the enhanced biomass of perennial grasses (PG). Higher resistance to drought and fast resource acquisition strategy might drive the rapid recovery and expansion of PG. Our findings revealed the rapid recovery of grasslands and the critical role of community overcompensation in maintaining grassland ecosystem function and stability under future climate change scenarios.

Herbivore assemblages affect soil microbial communities by altering root biomass and available nutrients in an alpine meadow.

Three different herbivore grazing assemblages, namely, yak grazing (YG), Tibetan sheep grazing (SG) and yak and Tibetan sheep co-grazing (MG), are practiced in alpine meadows on the Qinghai-Tibetan Plateau (QTP), but the effects of the different herbivore assemblages on soil microbes are relatively unknown. The microbial community plays an important role in the functional stability of alpine grassland ecosystems. Therefore, it is important to understand how the microbial community structure of grassland ecosystems changes under different herbivore grazing assemblages to ensure their sustainable development. To fill this gap, a field study was carried out to investigate the effects of YG, SG, and MG on plant communities, soil physico-chemical properties and microbial communities under moderate grazing intensity in alpine meadows. Grazing increased the β-diversity of the bacteria community and decreased the β-diversity of the fungal community. The herbivore assemblage affected the microbial community diversity, but not the plant community diversity. Total phosphorus, soil bulk density, root biomass, and plant α-diversity were correlated with both the bacterial and fungal community composition, available phosphorus and soil moisture were correlated only with the bacterial community composition, while available potassium and above-ground net primary production (ANPP) were correlated only with the fungal community composition. Soil available nitrogen, soil available phosphorus and soil bulk density were highest in SG, while ANPP was highest in MG. It was concluded that MG can improve ANPP and stabilize the soil microbial community, suggesting that MG is an effective method for sustainable use and conservation of alpine meadows on the QTP.

Canopy structure: An intermediate factor regulating grassland diversity-function relationships under human disturbances.

Grasslands are one of the largest coupled human-nature terrestrial ecosystems on Earth, and severe anthropogenic-induced grassland ecosystem function declines have been reported recently. Understanding factors influencing grassland ecosystem functions is critical for making sustainable management policies. Canopy structure is an important factor influencing plant growth through mediating within-canopy microclimate (e.g., light, water, and wind), and it is found coordinating tightly with plant species diversity to influence forest ecosystem functions. However, the role of canopy structure in regulating grassland ecosystem functions along with plant species diversity has been rarely investigated. Here, we investigated this problem by collecting field data from 170 field plots distributed along an over 2000km transect across the northern agro-pastoral ecotone of China. Aboveground net primary productivity (ANPP) and resilience, two indicators of grassland ecosystem functions, were measured from field data and satellite remote sensing data. Terrestrial laser scanning data were collected to measure canopy structure (represented by mean height and canopy cover). Our results showed that plant species diversity was positively correlated to canopy structural traits, and negatively correlated to human activity intensity. Canopy structure was a significant indicator for ANPP and resilience, but their correlations were inconsistent under different human activity intensity levels. Compared to plant species diversity, canopy structural traits were better indicators for grassland ecosystem functions, especially for ANPP. Through structure equation modeling analyses, we found that plant species diversity did not have a direct influence on ANPP under human disturbances. Instead, it had a strong indirect effect on ANPP by altering canopy structural traits. As to resilience, plant species diversity had both a direct positive contribution and an indirect contribution through mediating canopy cover. This study highlights that canopy structure is an important intermediate factor regulating grassland diversity-function relationships under human disturbances, which should be included in future grassland monitoring and management.

Autumn nitrogen enrichment destabilizes ecosystem biomass production in a semiarid grassland.

Nitrogen (N) deposition decreases the temporal stability of ecosystem aboveground biomass production (ecosystem stability). However, little is known about how the responses of ecosystem stability differ based on seasonal N enrichment. By adding N in autumn, winter, or growing season, from October 2014 to May 2020, in a temperate grassland in northern China, we found that only N addition in autumn resulted in a significantly positive correlation between ecosystem mean aboveground net primary productivity (ANPP) and its standard deviation and significantly reduced ecosystem stability. Autumn N-induced reduction in ecosystem stability was associated with the vanished negative effect of community-wide species asynchrony (asynchronous dynamics among populations to environmental perturbations) on the standard deviation of ecosystem ANPP in combination with the emerged positive effect of dominance (Simpson's dominance index that indicates the relative weight of dominant species in a community). Our findings indicate that autumn N addition might overestimate the negative effect of annual atmospheric N deposition on ecosystem stability, suggesting that to better evaluate the influence of N deposition in temperate grasslands, both field experiments and global modeling should consider not only the annual N load but also its seasonal dynamics. Moreover, further studies should pay more attention to the alteration in the ecosystem temporal deviations, which might be more sensitive to human-induced environmental changes.

Assessing multiple limiting factors of seasonal biomass production and N content in a grassland with a year-round production.

There is little evidence on the extent that multiple factors simultaneously limit ecosystem function of grasslands with year-round production. Here we test if multiple factors simultaneously limit (i.e., more than one factor at a time) grassland functioning in different seasons and how they interacted with N availability. In a Flooding Pampa grassland, we ran a separate factorial experiment in spring, summer, and winter with several treatments: control, mowing, shading, P addition, watering (only in summer), and warming (only in winter), each of them crossed with two nitrogen treatments: control and N addition. Grassland functioning was assessed by aboveground net primary productivity (ANPP), green and standing dead biomass, and N content at the species group level. Out of 24 potential cases (three seasons by eight response variables), 13 corresponded to just one limiting factor, 4 to multiple limiting factors, and the other 7 to no evidence of limitation. In conclusion, grassland functioning in each season was most often limited by just one factor, while multiple limiting factors were rarer. Nitrogen was the prevailing limiting factor. Our study expands our knowledge of limitations imposed by factors associated with disturbance and stress, such as mowing, shading, water availability, and warming in grasslands with year-round production.

Plant nitrogen retention in alpine grasslands of the Tibetan Plateau under multi-level nitrogen addition

Nitrogen (N) deposition might alleviate degradation of alpine grassland caused by N limitation on the Tibetan Plateau (TP). To determine such limitation and quantify the N-induced N retention in plant, a six-year fertilization experiment with six levels of N addition rates (0, 1, 2, 4, 8 and 16 g N m−2 yr−1) was conducted in the Namco alpine steppe and additional 89 experiments with multi-level N addition were also synthesized worldwide among which 27 sites were on the TP. In general, N addition promoted N retention in plants, and this increasing trend diminished at the critical N rate (Ncr). The maximum N retention capacity (MNRC) of plants at Ncr was strongly correlated with initial aboveground net primary productivity with a slope of 0.02, and the MNRC of grasslands globally ranged from 0.35 to 42.59 g N m−2 yr−1, approximately account for 39% of Ncr. Tibetan alpine grassland had a low average MNRC (2.24 g N m−2 yr−1) with distinct regional characteristic, which was much lower in the western TP (0.80 g N m−2 yr−1) than the eastern TP (4.10 g N m−2 yr−1). Our results inferred 0.33–1.21 Tg N yr−1 (0.22–0.79 g N m−2 yr−1) can be retained and 5.65–20.11 Tg C yr−1 (3.67–13.06 g C m−2 yr−1) can be gained by Tibetan alpine grasslands under current N deposition level. With the aggravation of N deposition, the alpine steppe ecosystem might continuously absorb N and C until N deposition reaches Ncr.

Responses of a semiarid grassland to recurrent drought are linked to community functional composition.

Recurrent droughts are an inevitable consequence of climate change, yet how grasslands respond to such events is unclear. We conducted a 6-year rainfall manipulation experiment in a semiarid grassland that consisted of an initial 2-year drought (2015-2016), followed by a recovery period (2017-2018) and, finally, a second 2-year drought (2019-2020). In each year, we estimated aboveground net primary productivity (ANPP), species richness, community-weighted mean (CWM) plant traits, and several indices of functional diversity. The initial drought led to reduced ANPP, which was primarily driven by limited growth of forbs in the first year and grasses in the second year. Total ANPP completely recovered as the rapid recovery of grass productivity compensated for the slow recovery of forb productivity. The subsequent drought led to a greater reduction in total ANPP than the initial drought due to the greater decline of both grass and forb productivity. The structural equation models revealed that soil moisture influenced ANPP responses directly during the initial drought, and indirectly during the subsequent drought by lowering functional diversity, which resulted in reduced total ANPP. Additionally, ANPP was positively influenced by CWM plant height and leaf nitrogen during the recovery period and recurrent drought, respectively. Overall, the greater impact of the second drought on ecosystem function than the initial drought, as well as the underlying differential mechanism, underscores the need for an understanding of how increased drought frequency may alter semiarid grassland functioning.

Effects of multi-resource addition on grassland plant productivity and biodiversity along a resource gradient.

The change of plant biodiversity caused by resource-enhancing global changes has greatly affected grassland productivity. However, it remains unclear how multi-resource enrichment induces the effects of multifaceted biodiversity on grassland productivity under different site resource constraints. We conducted a multiple resource addition (MRA) experiment of water and nutrients at three sites located along a resource gradient in northern China. This allowed us to assess the response of aboveground net primary productivity (ANPP), species (species richness and plant density), functional (functional richness and community-weighted mean of traits) and phylogenetic (phylogenetic richness) diversity to increasing number of MRA. We used structural equation model (SEM) to examine the direct and indirect effects of MRA and multifaceted biodiversity on ANPP. The combined addition of the four resources increased ANPP at all three sites. But with increasing number of MRA, biodiversity varied at the three sites. At the high resource constraint site, species richness, plant density and leaf nitrogen concentration (LNC) increased. At the medium resource constraint site, plant height and LNC increased, leaf dry matter content (LDMC) decreased. At the low resource constraint site, species, functional and phylogenetic richness decreased, and height increased. The SEM showed that MRA increased ANPP directly at all three sites, and indirectly by increasing plant density at the high constraint site and height at the medium constraint site. Independent of MRA, ANPP was affected by height at the high resource constraint site and LNC at the low resource constraint site. Our results illustrate that multi-resource addition positively affects productivity, while affects biodiversity depending on site resource constraint. The study highlights that site resource constraint conditions need to be taken into consideration to better predict grassland structure and function, particularly under the future multifaceted global change scenarios.

Presence of Access Roads Results in Reduced Growing Season Carbon Uptake in Adjacent Boreal Peatlands

AbstractWe conducted a 2‐year study to examine the impacts of resource access roads on carbon (C) exchange in two forested boreal peatlands (a bog and a fen). Along six transects (perpendicular to the road), at 2, 6, and 20 m from the edge of the road on both sides of the road (RI areas), we measured understory CO2 fluxes bi‐weekly from May to August 2016 and 2017 and compared this to measurements at reference areas at least 50 m from the road. Furthermore, we estimated aboveground biomass and net primary productivity of overstory shrubs and trees and combined that with understory fluxes to estimate annual net ecosystem carbon balance, and road‐induced C emissions. Overall, at the bog, the RI areas were sources of C in both 2016 (89.9 g C m−2 y−1) and 2017 (108.9 g C m−2 y−1) while reference areas were sinks. However, at the fen, both RI areas (−744.7, −310.9 g C m−2 y−1 in 2016 and 2017, respectively) and reference areas were sinks of C. Averaged across both peatlands, the estimated road‐induced C losses were ∼7.97 and 7.40 Mg C for each km of the road in 2016 and 2017, respectively. However, areas connected by culverts showed lower road‐associated impact on C emissions. Therefore, we suggest that industries and infrastructure developers align the road parallel to the local water flow direction, when possible, consider the hydrogeological setting during road design to reduce hydrologic impacts, and increase hydrological flows between up‐ and downstream by adequate culverts.

Patterns of net primary production changes in eurasian steppes

The aim of the study. The aim of the study was to analyze changes in the above-ground (ANP), below-ground (BNP) and total net primary production (NPP), expressed in dry matter, in meadow, true and dry steppes along the latitudinal (from 56o to 43o N) and longitudinal (from 36o to 116o E) gradients. Methodology. Production characteristics of 32 steppes (9 meadow, 14 true and 9 dry steppes), obtained by the same method of minimal estimate, were analyzed. Main results. The ANP value in meadow steppes decreases from 10,2 to 3,1 t/ha per year, in true steppes from 6,7 to 0,7 t/ha per year and in dry steppes from 3,7 to 0,6 t/ha per year. The value of BNP in meadow steppes varies from 26,8 to 10,1 t/ha per year; in true steppes - from 25.7 to 7.7 t/ha per year; and in dry steppes - from 24,8 to 4,9 t/ha per year. The BNP changes from West to East were found not to follow the ANP changes: a decrease in ANP may be accompanied by an increase in BNP. According to the ANP estimates the analyzed steppes can be grouped as following: 1) ANP from 10 to 5; 2) ANP from 5 to 3; 3) ANP from 3 to 1; 4) ANP less than 1 t/ha per year. The first group is located between 56o and 51o NL and includes six meadow steppes and one true steppe. The second group includes all three types of steppes (three meadow, six true and one dry steppe) between 56o and 50o N. The third group of steppes, between 54° and 43° NL, consists of six true and seven dry steppes. At 50°N one true and one dry steppes are located with the smallest ANP. The first and the second groups are located in the same territory (from 56o to 50o N) and include both meadow and true steppes. About 70% of the meadow and half of the true steppes are characterized by the ANP ranging from 6.7 to 3.1 t/ha per year. In the northern part of the explored zone there are highly productive meadow steppes, whereas in its southern part there are true steppes with both high and low production. The third group of steppes, with production from 3 to 1 t/ha per year, includes seven low-productive true and eight dry steppes. The average ANP of true and dry steppes of this group are similar (2,2 t/ha per year). Consequently, the area from 54° to 43°N can be considered as a zone of dry steppes. Conclusion. There are no separate zones of meadow and real steppes, but there is a steppe zone that includes meadow and true steppes. The proposed division of the steppes and their zoning is made on the basis of ANP, which is the most important characteristic of any ecosystem.

Short-term grazing changed temporal productivity stability of alpine grassland on Qinghai-Tibetan Plateau via response species richness and functional groups asynchrony

The stability of grassland is pivotal in maintaining the grassland functioning and services. However, the knowledge about the consequences of grazing on stability of grassland productivity is limited. Based on a 3-year manipulated experiment with two grazing regimes (i.e., continuous grazing and rotational grazing) along four levels of grazing-intensity (0, 4, 6, and 8 sheep per hectare) on the Qinghai-Tibetan Plateau, we researched the responses of temporal stability of plant community and functional groups of alpine grasslands to different grazing management regimes. We found that grazing regimes, intensity and their interaction affected the temporal stability of aboveground net primary productivity of alpine grassland (ANPP), and intermediate rotational grazing significantly reduced the temporal stability of ANPP, whereas increased the stability of productivity of functional group of forbs. The response species to continuous grazing and rotational grazing are different, for grasses and forbs respectively. Rotational grazing and intermediate continuous grazing increased the diversity of response species. Structural equation modeling further revealed that functional groups asynchrony stabilized the productivity of the alpine grassland ecosystem under grazing in the Qinghai-Tibetan Plateau. These results showed that the rotational grazing and intermediate continuous grazing can maintain the productivity stability, and highlighted importance of regulating the relationships among functional groups for promoting the stability of alpine grassland under grazing management.

Above- and belowground net-primary productivity: A field-based global database of grasslands.

Net primary productivity (NPP) over global grasslands is crucial for understanding the terrestrial carbon cycling and for the assessments of wild herbivores food security. During the past few decades, numerous field investigations have been conducted to estimate grassland NPP since the measuring criterion released by the International Biological Program. However, a comprehensive NPP database, particularly for belowground NPP (BNPP), in global grasslands is rare to date. Here, field NPP measurements from 438 publications (1957-2018) in global grasslands were collected, critically filtered, and incorporated in a comprehensive global database with observations for aboveground NPP (ANPP), BNPP, total NPP (TNPP), and BNPP fraction (fBNPP ). Associated information on geographical locations, climatic records, grassland types, land use patterns, manipulations subjected to manipulative experiments, sampling year of study sites, as well as NPP measurement methods are also documented. This database included 2985 entries from 1785 study sites. Among them, 806 entries contained paired data of ANPP and BNPP, resulting in the 806 fBNPP data. The study sites encompassed global grasslands with latitudinal range of 54.5° S~78.9° N, longitudinal range of 157.4° W~175.8° E, and altitudes from 0 to 5168 m above sea level, covering broad climatic gradients (-17.6 to 28.8°C in mean annual temperature and 63-2052 mm in mean annual precipitation). This global database is the world's largest paired data of ANPP and BNPP field measurements in grasslands. It can be used to study the spatio-temporal patterns of NPP and its allocation, evaluate the responses of above- and below-ground carbon components to future global changes, and validate the NPP estimation by empirical or process-based models in global grasslands. The database can be freely used for noncommercial applications. We kindly request users cite this data paper when using the database, respecting all the hard work during data compilation.

A research agenda for nonvascular photoautotrophs under climate change.

Nonvascular photoautotrophs (NVP), including bryophytes, lichens, terrestrial algae, and cyanobacteria, are increasingly recognized as being essential to ecosystem functioning in many regions of the world. Current research suggests that climate change may pose a substantial threat to NVP, but the extent to which this will affect the associated ecosystem functions and services is highly uncertain. Here, we propose a research agenda to address this urgent question, focusing on physiological and ecological processes that link NVP to ecosystem functions while also taking into account the substantial taxonomic diversity across multiple ecosystem types. Accordingly, we developed a new categorization scheme, based on microclimatic gradients, which simplifies the high physiological and morphological diversity of NVP and world-wide distribution with respect to several broad habitat types. We found that habitat-specific ecosystem functions of NVP will likely be substantially affected by climate change, and more quantitative process understanding is required on (1) potential for acclimation, (2) response to elevated CO2 , (3) role of the microbiome, and (4) feedback to (micro)climate. We suggest an integrative approach of innovative, multimethod laboratory and field experiments and ecophysiological modelling, for which sustained scientific collaboration on NVP research will be essential.

Multiple global change drivers show independent, not interactive effects: a long-term case study in tallgrass prairie.

Ecosystems are faced with an onslaught of co-occurring global change drivers. While frequently studied independently, the effects of multiple global change drivers have the potential to be additive, antagonistic, or synergistic. Global warming, for example, may intensify the effects of more variable precipitation regimes with warmer temperatures increasing evapotranspiration and thereby amplifying the effect of already dry soils. Here, we present the long-term effects (11 years) of altered precipitation patterns (increased intra-annual variability in the growing season) and warming (1°Cyear-round) on plant community composition and aboveground net primary productivity (ANPP), a key measure of ecosystem functioning in mesic tallgrass prairie. Based on past results, we expected that increased precipitation variability and warming would have additive effects on both community composition and ANPP. Increased precipitation variability altered plant community composition and increased richness, with no effect on ANPP. In contrast, warming decreased ANPP via reduction in grass stems and biomass but had no effect on the plant community. Contrary to expectations, across all measured variables, precipitation and warming treatments had no interactive effects. While treatment interactions did not occur, each treatment did individually impact a different component of the ecosystem (i.e., community vs. function). Thus, different aspects of the ecosystem may be sensitive to different global change drivers in mesic grassland ecosystems.

Responses of grassland productivity to mowing intensity and precipitation variability in a temperate steppe.

Mowing for hay is an important land use in grasslands that is affected by precipitation variability, due to the water-limited nature of these ecosystems. Past land use and precipitation conditions can have legacy effects on ecosystem functions, potentially altering responses to both mowing and precipitation. Nonetheless, it is still unclear how natural variation in precipitation will affect plant responses to changes in mowing intensity. We conducted a seven-year field experiment with three mowing intensity treatments compared to the traditional mowing intensity (5cm stubble height) as a control: increased mowing (2cm stubble), decreased mowing (8cm stubble) and ceased mowing. Decreased mowing increased both plant aboveground net primary productivity [ANPP] and forage yield across the whole community, driven by increases in graminoids, mainly owing to the positive response of plants to precipitation. Both mowing disturbance and precipitation variability had legacy effects on plant ANPP; however, these responses differed among the whole community, graminoid, and forb levels. Current-year community-wide ANPP [ANPPn] was positively associated with current-year precipitation [PPTn] in all mowing treatments, driven by positive precipitation responses of the dominant graminoids. For forbs, however, ANPPn was negatively associated with prior-year growing season precipitation [PPTn-1] across mowing treatments, potentially due to lagged competition with the dominant graminoids. Our results suggest that the response of the dominant graminoids is the primary factor determining the response of ANPP to mowing and precipitation variability in these grassland ecosystems, and highlight that decreasing mowing intensity may maximize both herder's income and grassland sustainability.

Below‐ground net primary productivity stability in response to a nitrogen addition gradient in an alpine meadow

Abstract Temporal stability of ecosystem productivity is important for providing reliable ecosystem services under global changes. Great efforts have been made to explore the response of above‐ground net primary productivity (ANPP) stability to nitrogen (N) enrichment, yet how it affects below‐ground net primary productivity (BNPP) stability remains elusive, which hinders a comprehensive understanding of ecosystem stability from the view of a whole system. Here, using a field manipulative experiment with six N addition rates (0, 2, 4, 8, 16, 32 g N m−2 year−1), we explored the response patterns and drivers of BNPP stability in the topsoil (0–20 cm) and subsoil (20–40 cm) in the alpine meadow. The results showed that BNPP stability at both soil depths showed a unimodal response to increasing N addition rates. Specifically, for both the topsoil and subsoil, low‐level N addition significantly promoted BNPP stability, while high doses of N addition had no significant impact on BNPP stability, suggesting that current low level of N deposition likely benefits the stable provision of below‐ground functioning. Furthermore, dominant species stability and species richness contributed most to the changes in BNPP stability in the topsoil, whereas only dominant species stability was the dominant driver of BNPP stability in the subsoil. This study is among the first to illuminate the main mechanisms underlying the responses of BNPP stability to N enrichment at various soil depths, which will advance our current understanding of N addition effects on below‐ground processes and benefit the sustainable provision of ecosystem functioning in the context of atmospheric N deposition. Read the free Plain Language Summary for this article on the Journal blog.

Responses of aboveground and belowground net primary productivity of ephemeral plants to extreme drought and extreme precipitation

To examine the effects of extreme drought event and extreme precipitation event on productivity of ephemeral plant, we experimentally reduced and increased growing season precipitation amounts by 65% across four slope positions and aspects along sand dunes in the southern edge of the Gurbantünggüt Desert. The results showed that extreme drought significantly reduced aboveground net primary productivity (ANPP) and belowground net primary productivity (BNPP) by 48.8% and 13.7%, respectively, and that extreme precipitation significantly increased ANPP and BNPP by 37.9% and 23.2%, respectively. The sensitivity of ANPP (0.26 and 0.21 g·m-2·mm-1) to extreme drought and extreme precipitation was significantly higher than that of BNPP (0.02 and 0.03 g·m-2·mm-1). In addition, ANPP (24.22 g·m-2) and BNPP (5.77 g·m-2) on the east side of sand dune were significantly increased by 29.7% and 71.7% compared with those on the west side. There was no significant difference in the sensitivity of ANPP and BNPP to precipitation change among different slope positions and aspects.

Grassland productivity responds unexpectedly to dynamic light and soil water environments induced by photovoltaic arrays

AbstractAgrivoltaic (AV) systems are designed to coproduce photovoltaic (PV) energy on lands simultaneously supporting agriculture (food/forage production). PV infrastructure in agroecosystems alters resources critical for plant growth, and water‐limited agroecosystems such as grasslands are likely to be particularly sensitive to the unique spatial and temporal patterns of incident sunlight and soil water inherent within AV systems. However, the impact of resource alteration on forage production, the primary ecosystem service from managed grasslands, is poorly resolved. Here, we evaluated seasonal patterns of soil moisture (SM) and diurnal variation in incident sunlight (photosynthetic photon flux density [PPFD]) in a single‐axis‐tracking AV system established in a formerly managed semiarid C3 grassland in Colorado. Our goals were to (1) quantify dynamic patterns of PPFD and SM within a 1.2 MW PV array in a perennial grassland, and (2) determine how aboveground net primary production (ANPP) and photosynthetic parameters responded to the resource patterns created by the PV array. We hypothesized that spatial variability in ANPP would be strongly related to SM patterns, typical of most grasslands. We measured significant reductions in ANPP directly beneath PV panels, where SM and PPFD were both low. However, in locations with significantly increased SM from the shedding and redistribution of precipitation by PV panels, ANPP was not increased. Instead, ANPP was greatest in locations where plants were shaded in the afternoon but received high levels of PPFD in the morning hours, when air temperatures and vapor pressure deficits were relatively low. Thus, contrary to expectations, we found relatively weak relationships between SM and ANPP despite significant spatial variability in both. Further, there was little evidence that light‐saturated photosynthesis (Asat) and quantum yield of CO2 assimilation (ϕCO2) differed for plants growing directly beneath (lowest PPFD) versus between (highest PPFD) PV panels. Overall, the AV system established in this semiarid managed grassland did not alter patterns of ANPP in ways predictable from past studies of controls of ANPP in open grasslands. However, our results suggest that the diurnal timing of low versus high periods of PPFD incident on plants is an important determinant of productivity patterns in grasslands.

Plant C:N ratio predicts community composition changes under N addition in an alpine meadow

Abstract Plant functional traits play important roles in determining plant responses to environmental change and further shaping community composition, but the role of plant stoichiometry remains poorly understood in regulating community responses to continually increased nitrogen (N) deposition. In this paper, we used a 5‐year manipulative experiment with six N addition rates (Nrate) to explore how the N response of different plant functional groups including forbs, grasses, sedges and legumes links to above‐ground plant carbon‐to‐N ratio (C:N, related to N use strategies) in an alpine meadow. We found that plant C:N explained 45.8% and 42.6% of N response variation among functional groups in plant above‐ground net primary productivity (ANPP) and abundance. Over increasing Nrate, functional groups with higher C:N (grasses and sedges) tended to grow better and have greater abundance, yet those with lower C:N (forbs and legumes) were at risk of loss, subsequently mitigating the N‐caused decline in community‐level plant C:N. This was mainly due to that functional groups with higher C:N not only possessed higher N use efficiency but also had greater competitiveness for above‐ground light due to higher plant height. In addition, we also found that plant C:N differences among functional groups remained relatively constant over Nrate, suggesting that the ability of this trait to indicate functional group‐specific N responses was stable. Synthesis. Our results show that the N responses of different herbaceous plants can be well explained by plant C:N. Thus, we suggest the prediction of plant community composition changes under N deposition would be greatly improved by considering this easily measured stoichiometric trait.