Abstract: Aims Climate change is predicted to cause both increased temperatures and changes in precipitation, leading to more severe droughts in some areas. How these changes will affect plant growth may depend in part on biotic context. Most vascular plants form symbiotic relationships with arbuscular mycorrhizal fungi (AMF), root symbionts that provide soil nutrients to plants in exchange for carbohydrates, which may reduce the effects of environmental stresses on plants. We investigated if AMF modified temperature and drought effects on plant growth, fitness and defenses against herbivory.
Methods We manipulated AMF presence, temperature and water availability on bell pepper plants (Capsicum annuum L.) in a field setting to measure plant growth and fitness responses. In a growth chamber experiment, we also investigated if AMF influenced insect herbivores feeding on plants at elevated temperatures.
Important findings Drought consistently reduced plant growth, and AMF did not change drought impacts. However, with sufficient water, AMF tended to benefit plant growth and flower production (but not fruit production) compared to non-mycorrhizal plants. In the growth chamber, temperature and AMF influenced plant protein and phosphorus contents, but not defensive chemistry or herbivore performance. Thus, AMF may ameliorate the effects of temperature stress due to climate change on plants by increasing growth and nutrient content, but these effects do not extend to the constitutive herbivory defenses examined here.

Key words: aboveground-belowground, arbuscular mycorrhizal fungi, climate change, drought, herbivore, indirect effects