Drought effects on montane grasslands nullify benefits of advanced flowering phenology due to warming

Time-Lag of Seasonal Effects of Extreme Climate Events on Grassland Productivity Across an Altitudinal Gradient in Tajikistan

Mountain grassland ecosystems around the globe are highly sensitive to seasonal extreme climate events, which thus highlights the critical importance of understanding how such events have affected vegetation dynamics over recent decades. However, research on the time-lag of the effects of seasonal extreme climate events on vegetation has been sparse. This study focuses on Tajikistan, which is characterized by a typical alpine meadow-steppe ecosystem, as the research area. The net primary productivity (NPP) values of Tajikistan's grasslands from 2001 to 2022 were estimated using the Carnegie-Ames-Stanford Approach (CASA) model. In addition, 20 extreme climate indices (including 11 extreme temperature indices and 9 extreme precipitation indices) were calculated. The spatiotemporal distribution characteristics of the grassland NPP and these extreme climate indices were further analyzed. Using geographic detector methods, the impact factors of extreme climate indices on grassland NPP were identified along a gradient of different altitudinal bands in Tajikistan. Additionally, a time-lag analysis was conducted to reveal the lag time of the effects of extreme climate indices on grassland NPP across different elevation levels. The results revealed that grassland NPP in Tajikistan exhibited a slight upward trend of 0.01 gC/(m2·a) from 2001 to 2022. During this period, extreme temperature indices generally showed an increasing trend, while extreme precipitation indices displayed a declining trend. Notably, extreme precipitation indices had a significant impact on grassland NPP, with the interaction between Precipitation anomaly (PA) and Max Tmax (TXx) exerting the most pronounced influence on the spatial variation of grassland NPP (q = 0.53). Additionally, it was found that the effect of extreme climate events on grassland NPP had no time-lag at altitudes below 500 m. In contrast, in mid-altitude regions (1000-3000 m), the effect of PA on grassland NPP had a significant time-lag of two months (p < 0.05). Knowing the lag times until the effects of seasonal extreme climate events on grassland NPP will appear in Tajikistan provides valuable insight for those developing adaptive management and restoration strategies under current seasonal extreme climate conditions.

Temperature and soil moisture manipulation yields evidence of drought-induced pollen limitation in bee-pollinated squash

Climate change alters environmental conditions in ways that directly and indirectly affect plants. Flowering plants, for example, modify reproductive allocation in response to heat and drought stress, and such changes can in turn affect pollinator visitation and, ultimately, plant reproduction. Although the individual effects of warming and drought on plant reproductive allocation are well known, these factors may interact to influence reproduction. Here, we conducted a fully crossed temperature by irrigation manipulation in squash (Cucurbita pepo) to test how temperature and soil moisture variation affect pollinator-mediated reproduction. To tease apart the direct and indirect effects of temperature and soil moisture, we compared hand-pollinated plants to bee-pollinated plants and restricted bee foraging (i.e., pollen transfer) to one experimental group per day. Temperature and soil-moisture limitation acted independently of one another: warming decreased flower size and increased pollen production, whereas the effects of soil-moisture limitation were uniformly inhibitory. While treatments did not change squash bee (Xenoglossa spp.) behavior, floral visitation by the honey bee (Apis mellifera) increased with temperature in male flowers and decreased with soil moisture in female flowers. Pollen deposition by bees was independent of plant soil moisture, yet reducing soil moisture increased pollen limitation. This result stemmed at least in part from the effects of soil-moisture limitation on pollen viability; seed set declined with increasing deposition of fluorescent pigment (a proxy for pollen) from plants experiencing decreased soil moisture. These findings suggest that the transfer of lower-quality pollen from plants experiencing soil-moisture limitation led to drought-induced pollen limitation. Similar effects may occur in a wide variety of flowering plant species as climate warming and drought increasingly impact animal-pollinated systems.

Stable plant community biomass production despite species richness collapse under simulated extreme climate in the European Alps

Direct observation of biodiversity loss in response to abrupt climate change can resolve fundamental questions about temporal community dynamics and clarify the controversial debate of biodiversity loss impacts on ecosystem functioning. We tracked local plant species loss and the corresponding change of aboveground biomass of native and non-native species by actively pushing mountain grassland ecosystems beyond their ecological thresholds in a five-year, multisite translocation experiment across the European Alps. Our results show that species loss (ranging from a 73 % to 94 % reduction in species richness) caused by simulated climate extremes (strong warming interacting with drought) did not decrease community biomass. Even without non-native species colonization, the community biomass of native species remained stable during native species richness collapse. Switching our research focus from local extinction in the face of climate change towards the beneficial impacts of persisting native species (in addition to novel plant-plant interactions) might yield insights on transformative opportunities for boosting climate resilience.