Hydrolase enzyme activities in a successional gradient of biological soil crusts in arid and semi-arid zones

Abstract

In arid and semi-arid regions, pioneer organisms form complex communities that penetrate the upper millimetres of the bare substrate, creating biological soil crusts (BSC). These thin crusts play a vital role in whole ecosystem functioning because they enrich bare surfaces with organic matter, initiate biogeochemical cycling of elements, modify hydrological cycles, etc., thus enabling the ground to be colonized by vascular plants. Various hydrolase enzymes involved in the carbon (cellulase, ß-glucosidase and invertase activities), nitrogen (casein-protease and BAA-protease activities) and phosphorus (alkaline phosphomonoesterase activity) cycles were studied at three levels (crust, middle and deep layers) of three types of BSCs from the Tabernas Desert (SE Spain), representing an ecological gradient ranging from crusts predominated by cyanobacteria to crusts predominated by lichens (Diploschistes diacapsis, Lepraria crassissima). All enzyme activities were higher in all layers of all BSCs than in the bare substrate. The enzymes that hydrolyze low molecular weight substrates were more active than those that hydrolyze high molecular weight substrates (cellulase, caseinprotease), highlighting the pioneering characteristics of the BSCs. The hydrolytic capacity developed in parallel to that of ecological succession, and the BSCs in which enzyme activity was highest were those under Lepraria crassissima. The enzyme activity per unit of total organic C was extremely high; the highest values occurred in the BSCs formed by cyanobacteria and the lowest in those formed by lichens, which 2 indicates the fundamental role that the primary colonizers (cyanobacteria) play in enriching the geological substrate with enzymes that enable degradation of organic remains and the establishment of more developed BSCs. The results of the study combine information on different enzyme activities and provide a clear vision of how biogeochemical cycles are established in BSCs, thus confirming the usefulness of enzyme assays as key tools for examining the relationship between biodiversity and ecosystem function in biological soil crusts.

Macromolecular and chemical features of the excreted extracellular polysaccharides in induced biological soil crusts of different ages

“…Since the establishment of the symbiosis between fungi and cyanobacteria is based on the capability of the latter microorganisms to release simple sugars, the increase in the amounts of fructose and glucose in the soil through the hydrolysis of sucrose could also facilitate the interaction between cyanobacteria and fungal hyphae, ("attraction of beneficial organisms"), leading to the formation of the lichen bodies (Belnap, 2002;Miralles et al, 2012).…”

“…Notwithstanding the key role of BSCs in starting and enhancing biogeochemical cycles on bare substrates and in increasing soil total organic carbon (TOC), a limited number of studies have been so far addressed to analyze enzymatic activity in crusted soils (Miralles et al, 2012, and references therein), especially enzymatic activity of BSCs at different developmental stages. In this connection, it is worth stressing that the activity of dehydrogenase in the soil can provide correlative information on microbial activity and microbial populations, and in many cases it is related to soil organic matter content (Dormaar et al, 1984).…”

Capacity of biological soil crusts colonized by the lichen Diploschistes to metabolize simple phenols

“…In arid environments, these compounds help to protect colonizing organisms from environmental changes because, amongst other functions, their presence favours nutrient sequestration and soil hydrology, and decreases soil erodibility (Mager 2010;Mager and Thomas 2011). Furthermore, the low capacity of the biocrusts to degrade carbohydrates would explain the lower specific activity of invertase (one of the hydrolytic enzymes involved in the degradation of these compounds) in the biocrusts than in soils under Mesic and Mediterranean climates (Miralles et al 2012a). However, and although this fact appears to suggest a low level of enzymatic activity in the biocrust, the large decrease in Folin-Ciocalteu-reactive compounds as the moisture increases ( Fig.…”

“…The main types of soil are Epileptic and Endoleptic Leptosols, Calcaric Regosols and Eutric Gypsisols (ISSS Working Group WRB 1998). The geological substrate (analyzed according to the methods described in Guitián and Carballas 1976) has a silty loam texture, a pH (1:2.5 soil water extract) ranging from 6.7 to 8.7, and a calcium carbonate equivalent ranging from 11 to 30 % (Miralles et al 2012a).…”

Responses of temporal and spatial variation in soil respiration to biotic and abiotic factors in a desert shrubland in northwest China

“…T s and SWC) complex. Biological soil crusts are also inactive and exhibit C release most (90%) of the year to withstand extreme environment conditions (Miralles et al, 2012). They are metabolically active and exhibit CO 2 uptake within 20 min after moistened by dew, fog or rainfall (Lange et al, 2001;Barker et al, 2005;Grote et al, 2010;Su et al, 2011).…”