Changing climates can cause shifts in temperature and precipitation, resulting in warming and drought in some regions. Although each of these factors has been shown to detrimentally affect forest ecosystems worldwide, information on the impacts of the combined effects of warming and drought is lacking. Forest trees rely on mutualistic root-associated fungi that contribute significantly to plant health and protection against climate stresses. We used a six-year, ecosystem-scale temperature and precipitation manipulation experiment targeted to simulate the climate in 2100 in the Southwestern United States to quantify the effects of drought, warming and combined drought and warming on the root colonization (abundance), species composition and diversity of ectomycorrhizal fungi (EMF), and dark septate fungal endophytes in a widespread woodland tree, pinyon pine (Pinus edulis E.). Our results show that pinyon shoot growth after 6 years of these treatments was reduced more by drought than warming. The combined drought and warming treatment reduced the abundance and diversity of EMF more than either treatment alone. Individual ectomycorrhizal fungal taxa, including the drought tolerant Cenococcum geophilum, were present in all treatments but the combined drought and warming treatment. The combined drought and warming treatment also reduced the abundance of dark septate endophytes (DSE), but did not affect their diversity or species composition. The current year shoot growth of the trees correlated positively with ectomycorrhizal fungal diversity, highlighting the importance of diversity in mutualistic relationships to plant growth. Our results suggest that EMF may be more important than DSE to aboveground growth in P. edulis, but also more susceptible to the negative effects of combined climate stressors.

气候变化会引起温度和降水的变化，从而导致某些地区的变暖和干旱。尽管已显示所有这些因素都对全世界的森林生态系统产生不利影响，但仍缺乏有关变暖和干旱综合影响的信息。林木依靠与根系互生的互生真菌，这些真菌对植物健康和抵御气候胁迫具有重要作用。我们使用了一项为期六年的生态系统规模温度和降水操纵实验，旨在模拟美国西南部2100年的气候，以量化干旱，变暖以及干旱和变暖的综合影响对根部定殖（丰度），物种组成的影响广泛的林木中的外生菌根真菌（EMF）和深色分隔真菌内生菌的多样性美味松E.）。我们的结果表明，经过6年的干旱处理后，Pinyon笋的生长受干旱的影响比受暖影响的减少得更多。干旱和变暖的综合处理比单独的任何处理都减少了EMF的丰度和多样性。单个外生菌根真菌类群，包括耐旱性嗜水球藻除干旱和增温处理外，所有处理均存在。干旱和加温相结合的处理方法也减少了深色分隔的内生菌（DSE）的含量，但并未影响其多样性或物种组成。今年树木的新梢生长与外生菌根真菌多样性呈正相关，突出了在相互关系中多样性对植物生长的重要性。我们的结果表明，EMF可能比DSE更重要的是紫罗兰，但也更容易受到综合气候压力因素的负面影响。