全球变暖对土壤病原真菌维持森林树种多样性纬度格局的影响

Global warming is well recognized as a primary threat to biodiversity. A large number of studies have focused on the direct effect of global warming on biodiversity. However, little is understood how increasing temperature would affect the interactions between the soil-borne fungal pathogens and their plant hosts, i.e., the so-called Janzen-Connell effect (the JC effect) that is widely known to maintain biodiversity. In the temperate zone, winter temperature is a factor limiting pathogen growth – more than 99% of fungal pathogen populations fail to overwinter. In contrast, there is no winter cold spell in the tropical area. Therefore, the effect of global warming on the JC effect is predicted to vary along the latitude: stronger in the temperate forests but weaker in the tropical forests. This study is proposed to test this prediction. We design to select three study sites: Jianfengling plot on Hainan Island (tropical montane forest), Heishiding plot in Guangdong Province (subtropical evergreen broad-leaved forest), and Changbaishan plot in Jilin Province (temperate mixed conifer broad-leaved forest). We will firstly compare the intensity of the JC effect and host-specificity of soil-borne fungal pathogens along the latitude, whereby providing empirical evidence showing the role of soil-borne fungal pathogens in regulating the observed biodiversity in the study sites. We will further establish open top chamber (OTC) warming experiments to emulate global warming predicted by IPCC. The OTC experiment will allow us to quantify the warming effect on fungal pathogenicity on host plants (i.e., the JC effect). This study is expected to significantly contribute to understanding the effects of global warming on soil-borne pathogens in maintaining the latitudinal pattern of biodiversity in forests.

当前以全球变暖为特征的气候变化已成为生物多样性维持的新威胁。已有研究主要集中在物种对全球变暖的直接响应，但全球变暖对生物多样性的威胁更多的通过物种间的相互作用间接影响生物多样性。大量研究证实土壤病原真菌引起的Janzen-Connell效应（JC效应）对维持森林物种多样性具有重要贡献，但球变暖背景下JC效应强度如何变化进而对森林树种多样性的影响有待探讨。近期预实验还发现不同纬度土壤病原真菌对升温的响应不同。因此，本项目拟选择具有明显纬度梯度的热带雨林、亚热带常绿阔叶林和温带阔叶红松林为研究对象。通过控制实验比较不同纬度JC效应强度以及土壤病原真菌寄主专化性的差异，为土壤病原真菌促进森林树种多样性纬度梯度格局提供科学依据。在此基础上，着重分析升温对JC效应强度以及土壤病原菌寄主专化性的改变，探讨全球变暖对土壤病原菌维持森林树种多样性梯度格局的影响，为生物多样性保育及应对全球变暖提供新的视角。

全球变暖对生物多样性的影响受到越来越多的关注，但以往的研究主要关注气温上升对植物的直接影响，而忽视了全球变暖通过改变物种间（植物-地下微生物）的相互作用进而间接地影响植物多样性。本项目围绕土壤病原真菌引起的Janzen-Connell效应促进森林树种共存这一理论，并结合经典的植物病害三角框架（即病害的发生需要病原菌在合适的环境条件下遇到宿主植物以及植物病害发生的严重程度受环境条件调控），探讨升温对Janzen-Connell效应强度改变。结合在温带地区多达99%的病原真菌群落不能成功越冬以及暖冬后植物病害严重程度会显著增加，而在热带地区没有这一寒冷天气的胁迫，从而可以预测在不同的维度地区升温对Janzen-Connell效应的影响也将是不同的。.为验证这一预测，本项目选取了具有明显纬度梯度格局的热带雨林（海南省尖峰岭）、亚热带常绿阔叶林（广东省黑石顶）和温带阔叶红松林（吉林省长白山）为研究对象。通过野外原位升温实验（OTCs；开顶箱），研究升温在不同的纬度区对Janzen-Connell效应强度的改变，同时探讨了升温对土壤病原真菌寄主专化性的影响。在吉林长白山、广东黑石顶和海南尖峰岭三个实验地点OTC的升温能力分别为1.20 ± 0.53°C、1.66±1.11 °C和 0.89±0.42 °C。OTC的升温能力均能满足了申请书的预期。研究结果发现，在温带地区升温可以增加病原菌引起的幼苗死亡率，升温后土壤病原菌相对多度增加是引起幼苗死亡的增加的主要原因；而在热带地区却得到截然不同相反的结果，即升温降低了病原菌引起的幼苗死亡率，与升温降低了病原菌相对多度的预测一致。.该研究将增加我们对气候变暖背景下生物多样性维持机制的了解，进而更好地预测未来气候变暖背景下沿纬度梯度下森林生物多样性的变化，为生物多样性保育及应对全球变暖提供新的视角。