Hotspot enlargement and shortening hot moments in the rhizosphere to acquire labile phosphorus from fungal necromass in response to warming effects

Abstract

Fungal necromass is a potential energy and nutrient source for microorganisms and plants, yet the elevated temperature accelerates turnover rate of this source while enhances plant nutrient demand. However, a critical question that remains inadequately addressed is whether fungal necromass can be utilized to offset the effects of warming on plant nutrient demand, helping to sustain plant growth in changing climates. In this study, two maize varieties, including a wild-type and root-hair-defective rth3 mutant, were grown in phosphorus (P) deficient soil at temperatures of 20 °C and 30 °C to detect the mechanisms driving the fungal necromass turnover under warming effects and plant root genotypes. By applying in situ zymography, we observed that the percentage of hotspot area in the rhizosphere increases by 65–82 % with a 10 °C temperature rise. However, when fungal necromass was introduced to the soil, the hotspot percentage at 20 °C was 44–116 % higher compared to 30 °C. Additionally, the addition of necromass significantly enlarged the hotspot percentage as compared to zero necromass treatment, particularly at 20 °C. The shorter turnover time of soil organic matter (SOM) at 30 °C compared to 20 °C, following the addition of fungal necromass, clearly indicated that the combined effects of warming and added necromass-derived C and P compounds accelerated SOM decomposition. The formation of a fish-bone root structure in the maize mutant could be a compensatory strategy in response to the absence of root hairs under warming conditions. These fish-bone roots potentially enhanced the acquisition of labile C and P from the added fungal necromass. Furthermore, the unchanged K_m but increased V_max in necromass-treated soil under 30 °C suggested that microorganisms allocate their energy resources to synthesizing more enzymes rather than increasing enzyme efficiency in response to warming stress. Overall, as an easily decomposed substances, fungal necromass mediates the response of the dynamic interactions between plants and microorganisms to rising temperature by enlarging the hotspot percentage by 88 % but shortening duration of organic matter decomposition up to 125 %. Therefore, these processes can be considered as the adaptation of agro-ecosystems to global warming.