Species richness: a pivotal factor mediating the effects of land use intensification and climate on grassland multifunctionality

Temperate semi-natural grasslands harbour unique biodiversity, support
livestock farming through forage production, and deliver many essential
ecosystem services (ESs) to human society; they are highly
multifunctional. However, temperate grassland ecosystems are also among
the most threatened ecosystems on earth due to land use and climate
change. Understanding how biodiversity, climate, and land use
intensification impact grassland multifunctionality through complex direct
and indirect pathways is critical to better anticipate the future of these
fragile ecosystems.  Here, we evaluate how local plant species
richness (SR) modulates the effect of land use intensification and climate
on grassland multifunctionality (using six key ESs: biomass productivity
and stability, forage quality, carbon storage, pollination, and local
plant rarity) in the French Massif Central, the largest grassland in
Western-Europe. We sampled 100 grassland fields with contrasted
fertilisation rates, and SR over large elevational and latitudinal
gradients related to variation in mean annual temperature (MAT), and
drought severity (DS), two key climate change drivers that are predicted
to increase in the future. Using a confirmatory path analysis, we found
that SR was the main driver of multifunctionality. We also found
significant SR × MAT and SR × fertilization interactions suggesting that
warm climate and high fertilization rates may alter the
biodiversity-ecosystem multifunctionality relationships. Furthermore,
increasing temperature and fertilization indirectly influenced
multifunctionality by decreasing SR and consequent multifunctionality in
warm low-land and highly fertilized grasslands compared to colder montane
grasslands or less fertilised ones. DS only impacted some ES individually
(e.g. forage quality). Synthesis and applications: we identified SR as a
pivotal factor mediating the effects of land use intensification and
climate on multifunctionality through both direct and indirect pathways.
Failing to account for changes in SR could thus bias any prediction of –
or aggravate – the effects of land use intensification and climate change
on ESs delivery in temperate grassland ecosystems. Considering that SR,
MAT, and fertilization are major proxies of three main global change
drivers (biodiversity loss, climate change, and land use intensification)
our study may help to better anticipate the effect of multiple interacting
global change drivers on grassland ecosystems.

温带半自然草地孕育着独特的生物多样性，通过饲草生产支撑畜牧业发展，并为人类社会提供多种关键生态系统服务（ESs），具有高度的多功能性。然而，受土地利用和气候变化影响，温带草地生态系统也是地球上最受威胁的生态系统之一。理解生物多样性、气候和土地利用集约化如何通过复杂的直接与间接路径影响草地多功能性，对于更好地预测这些脆弱生态系统的未来至关重要。本研究以西欧最大的草地——法国中央高原为区域，评估了本地植物物种丰富度（SR）如何调节土地利用集约化与气候对草地多功能性的影响（采用6项关键ES指标：生物量生产力与稳定性、饲草质量、碳储存、传粉及本地植物稀有性）。我们在具有显著施肥梯度的100块草地开展采样，结合与年平均温度（MAT）和干旱严重程度（DS）变化相关的大尺度海拔与纬度梯度（这两项是未来预计加剧的关键气候变化驱动因素），分析了SR的作用。通过验证性路径分析，我们发现SR是草地多功能性的主要驱动因素。此外，SR与MAT、SR与施肥之间存在显著交互作用，表明温暖气候和高施肥水平可能改变生物多样性-生态系统多功能性关系。进一步研究显示，与寒冷山地草地或低施肥草地相比，在温暖低地和高施肥草地中，温度升高和施肥增加通过降低SR间接影响多功能性，进而导致多功能性下降。DS仅对部分ES产生单独影响（如饲草质量）。综合与应用：我们确定SR是通过直接和间接路径介导土地利用集约化与气候对多功能性影响的关键因素。若未考虑SR的变化，可能会偏差对温带草地生态系统中土地利用集约化和气候变化影响ES供给的预测，或加剧这些效应。鉴于SR、MAT和施肥分别是生物多样性丧失、气候变化和土地利用集约化这三大全球变化驱动因素的主要代理指标，本研究或有助于更好地预测多种相互作用的全球变化驱动因素对草地生态系统的影响。