Early response of soil fungal communities to the conversion of monoculture cropland to a temperate agroforestry system

Abstract

Background Alley-cropping systems in the temperate zone are a type of agroforestry in which rows of fast-growing trees are alternated with rows of annual crops. With numerous environmental benefits, temperate agroforestry is considered a promising alternative to conventional agriculture and soil fungi may play a key in maintaining productivity of these systems. Agroforestry systems that are established for more than 10 years have shown to increase the fungal biomass and impact the composition of soil fungal communities. Investigations of soil fungi in younger temperate agroforestry systems are scarce and the temporal dynamic of these changes is not understood. Methods Our study was conducted in a young poplar-based alley cropping and adjacent monoculture cropland system in an Arenosol soil in north-west Germany. We investigated the temporal dynamics of fungal populations after the establishment of agroforestry by collecting soil samples half, one, and one and a half years after conversion of cropland to agroforestry. Samples were collected within the agroforestry tree row, at 1, 7, and 24 m distance from the tree row within the crop row, and in an adjacent conventional monoculture cropland. The biomass of soil fungi, Asco-, and Basidiomycota was determined by real-time PCR. Soil fungal community composition and diversity were obtained from amplicon sequencing. Results Differences in the community composition of soil fungi in the tree row and arable land were detected as early as half a year following the conversion of monoculture cropland to agroforestry. In the tree row, soil fungal communities in the plots strongly diverged with the age of the system. The presence of young trees did not affect the biomass of soil fungi. Conclusions The composition of soil fungal communities responded rapidly to the integration of trees into arable land through agroforestry, whereas the fungal biomass was not affected during the first one and a half years after planting the trees. Fungal communities under the trees gradually diversified. Adaptation to spatially heterogeneous belowground biomass of the trees and understory vegetation or stochastic phenomena due to limited exchange among fungal populations may account for this effect; long-term monitoring might help unravelling the cause.

Abundance, Diversity, and Function of Soil Microorganisms in Temperate Alley-Cropping Agroforestry Systems: A Review

“…Other popular methods to characterize soil microbial communities in temperate agroforestry systems include substrate-induced respiration [ 27 , 39 , 46 , 52 ] and phospholipid fatty acids (PLFA) analysis [ 27 , 40 , 50 , 53 ]. More recently, modern molecular techniques such as real-time PCR [ 30 , 32 , 33 , 35 , 36 , 37 , 38 , 54 ] and amplicon sequencing [ 30 , 31 , 32 , 33 , 34 , 37 , 55 , 56 ] have been applied to study the soil microbiome of temperate agroforestry systems. Since the late 1990s, these and other tools have generated a large body of literature regarding the abundance, diversity, and function of soil microbial communities in temperate alley-cropping agroforestry systems that we review in this article.…”

“…The increase in the fungal population size through tree rows has not (yet) been detected in young agroforestry systems (less than five years of age) [ 33 , 36 ], and thus, appears to be limited to older systems. While a few studies showed no alteration of the fungi–to–bacteria ratio [ 27 , 54 ], several studies reported an increase in the ratio in the trees rows of agroforestry systems [ 35 , 38 , 39 , 50 , 57 ], suggesting that fungi benefit more from agroforestry practice than bacteria.…”

“…Tree rows in temperate alley-cropping systems strongly shape soil fungal communities and the effects partly extend into the crop rows [ 37 ]. Furthermore, the integration of poplar tree rows in arable land has been shown to alter the community composition of soil fungi as soon as six months after agroforestry establishment [ 33 ], indicating a rapid adaption of soil fungi to the trees.…”

“…In 2016, Banerjee and colleagues [ 30 ] published the first study that investigated soil bacterial communities in temperate agroforestry systems using 454 pyrosequencing. From 2019 onwards, several studies that used Illumina sequencing to profile microbial communities were published [ 31 , 32 , 33 , 34 ]. The work of Banerjee and colleagues [ 30 ] was also the first to quantify soil microbial groups in temperate agroforestry systems by using real-time PCR.…”

Fungal Indicators of Sensitivity and Resistance to Long-Term Maize Monoculture: A Culture-Independent Approach

“…Considering the complexity of the process of selecting appropriate indicators, at the beginning they were divided into biotic and abiotic indicators of soil health. The biotic indicators may include but are not limited to total biomass, activities, functioning, community composition, and interactions of soil-inhabiting macroorganisms and microorganisms that determine the trophic or food-web complexity of soil ecosystems ( Pervaiz et al, 2020 ; Behnke et al, 2021 ; Beule and Karlovsky, 2021 ; Neupane et al, 2021 ). The abiotic indicators of soil health include but are not limited to soil aggregation, aggregate stability, organic C and organic matter contents, nutrient cycling and sequestration, the composition of soil exudates and metabolites, nutrient balance, and other essential properties such as pH and CEC ( Pervaiz et al, 2020 ; Behnke et al, 2021 ).…”