Work package 3

Title

Field microplot experiments to unravel regulating processes

 

Objectives

  • To assess current biophysical conditions in healthy, partly-degraded and strongly degraded selected plant-soil systems in each of the study sites.
  • To determine the effects of imposed drought on plant-soil ecosystem functioning, including facilitation and competition between plants, and how these processes affect plant resource use, survival and growth.

 

Description of work and role of partners

The objective of WP3 is to unravel the complex processes that occur at the level of individual plants and surrounding bare soil in dryland ecosystems. Field microplot experiments will be used to investigate the effects of droughts on changes in the soil-plant system. Key processes are water and nutrient availability, and effects of direct surroundings in providing water and/or nutrients, including effects on plant facilitation and competition. The results of WP3 will be used to support the spatial and dynamic description of catastrophic shifts in the integrated soil-water-plant models to be developed in WP6 and parameterize them, and they will also provide knowledge that can help interpret the results of experiments in WP4 and 5.

 

Task 1: Ecosystems selection
Select typical plant-soil ecosystems from the dryland areas identified in WP2. In the past decades these areas have suffered from catastrophic shifts in plant and soil quality, biodiversity and ecosystem services due to the climate and human induced drivers defined in WP2. The hypothesis is that these plant-soil ecosystems are most sensitive to changes in abiotic conditions due to climate change and/or land use change. For each study site, 1 representative plant-soil combination will be selected. Based on the historic evolution of dryland ecosystems in WP2, trajectories of changes will be defined which have led to catastrophic shifts in plant-soil ecosystems in the past.

 

Task 2: Assessment of selected ecosystems

Based on the results of task 1, intact, partly degraded (with vegetation patches) and strongly degraded plant-soil ecosystems from natural sites will be selected. In each of these sites small plots (a few m2) will be used to determine plant available nutrients, organic matter and water content at a high spatial resolution in vertical transects across the plant-soil system. Plant phenology and productivity will also be studied, as well as microbial activity. This type of sampling will be undertaken on a monthly or bi-monthly basis to investigate changes during a one year cycle in dependence of the sequence of weather conditions. Also, a TDR (time domain reflectrometry) system will be used in the partly affected ecosystem to continuously measure water content below plants/tussocks and surrounding bare soil to study plant available water over time. The knowledge obtained in this way will be analysed to understand the processes that are operating at plant level, including those of facilitation and competition.

 

Task 3: Performing experiments on selected ecosystems

To simulate the effect of drought, part of the selected plots will be covered for different time periods to artificially impose severe drought and study effects on the plant-soil system. To minimise other effects the cover will be fully translucent, and will be supported by poles only (no walls). To prevent the influence from lateral influx of water from the surrounding area, metal sheets will be inserted into the ground around the plot. The same measurement procedure as described in task 2 will be used to study the difference with uncovered plots. The effects on the vegetation will also be studied, and periodic pictures will be taken to see the development of plants over time. This will enable us to find, under natural conditions, critical changes that occur in either plants or soil before catastrophic shifts occur and to define indicators that can be used to provide early warning signals.