Abstract
Arbuscular mycorrhizal fungi (AMF), symbionts with most terrestrial plants, produce glomalin-related soil protein (GRSP), which plays a major role in soil structure and quality. Both fungi hyphae and protein production in soils are affected by perturbations related to land-use changes, implying that GRSP is a sensitive indicator of soil quality. Unfortunately, GRSP degrades within years to decades in oxic environments, preventing its use as palaeoecological proxy. However, GRSP is transported to marine, near-shore anoxic sediments, where it accumulates and remains non-degraded, enabling the assessment of its potential as a palaeoecological proxy for soil ecosystem's health. Exploiting this fact, we have obtained for the first time a long-term record (c. 1250years) of GRSP content using a Posidonia oceanica seagrass mat sediment core from the Western Mediterranean (Portlligat Bay, Spain). The trends in GRSP content matched well with land-use changes related to agrarian activities reconstructed by pollen analysis. In periods of cultivation, GRSP accumulation in the mat decreased. Given the role played by GRSP, the results suggest that agrarian intensification may have resulted in perturbations to soil quality. Thus, GRSP in seagrass mat sediments can be used to assess long-term trends in continental soil quality induced by human activities. These findings open new possibilities in long-term ecology research, as other anoxic environments could be potentially valid too. Testing them would open the possibility to identify long-term patterns in soil quality and other environmental stressors that could also affect AMF and GRSP production in soils.
Highlights
Unravelling the potential of new palaeoecological proxies providing information on when a system has been disturbed is challenging
Glomalin-related soil protein record in the seagrass mat glomalin-related soil protein (GRSP) had an average content of 0.080 ± 0.005, with minimum and maximum values of 0.027 and 0.161 respectively
We did not find a decreasing trend of GRSP content and IR% with depth (Fig. 2b), which indicates that variations in GRSP might be driven by
Summary
Unravelling the potential of new palaeoecological proxies providing information on when a system has been disturbed is challenging. Other transformations that can be identified in present landscapes have passed unnoticed in the palaeoecological record, even when they could be useful to detect long-term variations in soil quality due to land-use change. One of them is the alteration of hyphae production by arbuscular mycorrhizal fungi (AMF), which are symbionts with the roots of most terrestrial plants and play a significant role in soil ecosystems' functioning (Wright et al, 2006). As land-use alters AMF communities, affecting GRSP production and its soil concentration (Wright et al, 1999), it is considered that the more GRSP in a soil the better the soil quality (Shrestha Vaidya et al, 2011), providing information on the health of a given soil ecosystem
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