Dr. Jasper Wubs

Plant and soil community development during two decades of nature restoration (CLUE)

2017-present, collaborators: Martijn Bezemer, Gerard Korthals, Maddy Thakur, Wim van der Putten.

Most studies of belowground (and aboveground) community development (succession) are based on chronosequences, which study temporal community dynamics through a space-for-time substitution approach. While many valuable insights have been gleaned from this apporach, we lack continuous monintoring projects to test these insights in real timeseries. In this project we use >20 years of plant and soil nematode community composition and abundance data to study how above- and belowground communtiies assemble during secondary succession after agricultural activities are ceased.

Phytobiome interactions in range expanding plants across a latitudinal gradient in Europe (ERC Advanced to WvdP).

2018-present, collaborators: Basten Snoek, Stefan Geisen, Kelly Ramirez, Rutger Wilschut, Marta Manrubia, Wim van der Putten.

Here we study using network analyses how soil microbiomes as well as aboveground insect communities (dis)assemble during range expansion.

Plant-soil community coupling across a >3000 km arditity gradent in Inner Mongolia, China

2018-present, collaborators: Xiong Dan, Wei Cunzheng, Ciska Veen, Wim van der Putten

In this collaborative project we study how plant and soil communtiies, with a special focus on nematodes, change along an extremly wide precipitation gradient in northern China.

Global synthesis of bottom-up and top-down controls on soil carbon stocks (NIOO strategic fund)

2017-2018, collaborators: Ciska Veen, Liesbeth Bakker, Judith Sitters, Tom Crowther, Wim van der Putten

Here we use the experimental sites of the globally distributed Nutrient Network to study the combined impacts of herbivore grazing and nutrient fertilization on soil carbon and nitrogen stocks in (semi-)natural grasslands. Earlier studies show that these effects depend highly on the ecological context, e.g. soil texture, climate etc, and by using the wide range of environmental conditions encompassed within NutNet we will gain an improved understanding of these context dependencies. For instance, we found that soil carbon stocks in grasslands are not particularly nitrogen-limited, but in fact co-limitation by potassium (and potentially other micronutrients) is much more important, particularly in dry climates and sandy soils (Crowther et al. in review). In addition, grazing impact on soil C and N are highly variable across the globe, but grazing tends to increase soil C and N in colder, more seasonal climates (Sitters et al. In prep).

Soil heterogeneity as a key to restoring nature and biodiversity on former arable fields (NWO, Biodiversiteit werkt)

2012-2017, collaborators: Martijn Bezemer, Wim van der Putten, Machiel Bosch (Natuurmonumenten)
The biodiversity of soils is enormous and soil organisms are essential determinants of the diversity and composition of plant communities. My PhD project focussed on the role of heterogeneity in soil biota on the restoration of natural grasslands on former arable fields. We investigated how spatial variation in and diversity of soil organisms changes during nature restoration and how soil inoculation may aid this process. In collaboration with the ‘Vereniging Natuurmonumenten” – a major Dutch nature conservation NGO – we studed this in a replicated field experiment and a chronosequence of grasslands on former arable fields in the Veluwe (NL) area.

In this field experiment we found that depending on the soil inoculum used (i.e. a dry heathland or a mesic grassland) the vegetation developed in the direction of the respective donor communities and the same was true for the soil communities in those treatments (e.g. microbes, nematodes). Naturally, this strong effect on ecosystem development is in part mediated by the input of seeds. However, in a companion experiment, we replicated the field treatments, except we added the same standardized seed mixture of 30 plant species to all treatments. In this companion experiment we found the same results as in the field, mesocosms treated with different soil inocula developped in the direction of the donor community. This thus shows that next to seed effects, also the soil community is importantly affecting the direction of ecosystem development in terms of plant species composition (Wubs et al 2016 Nature Plants).

Fig. Different soil inocula drove the development of the local vegetation in the direction of the donor communities.
 

Spatial consequences of individual plant-soil feedbacks

While soil-inoculation may help to reshape ecological communities by altering the general feedback between the vegetation and the soil communities, individual plants establishing in the field also generate their own plant-soil feedbacks. As plants grow they interact with the biota in the soil, which in turn with affect the performance of the plant. However, what the consequences of those plant-soil feedbacks are when neighbouring plants experience heterogeous feedbacks, the situation out there in the field, is unclear.

We conducted a greenhouse experiment where we explicitly manipulated the spatial heterogeneity of the plant-soil feedbacks. For monocultures we found that the plants on average grew less well (7% for shoot, 17% for roots) when grown in spatially heterogeneous soil than we ecpected based on the spatially homogeneous controls (Wubs & Bezemer 2016 J Ecol). In addition, we found that in mixtures of plants (i.e. experimental communities) heterogeneously conditioned soils led to a high plant diversity (Wubs & Bezemer 2018 Funct Ecol). However, this effect was not due to the spatial configuration of the conditioned soils, but was determined by the number of plant species that conditioned the soil initially. Consequently, soil conditioning by multiple species seems to promote plant diversity. In both monocultures and mixtures we found strong negative conspecific plant-soil feedbacks, and plant performance was more strongly correlated with fungal community composition than with soil abiotic conditions. Therefore, these results are in line with the hypothesis that at local spatial scales plant alpha diversity is regulated by species specific soil-borne pests, i.e. the Janzen-Connell or pest pressure hypothesis.

In a next expriment, we tested how conspecific and heterospecific plant-soil feedbacks carry-over in time. We found that important interactions exist between the most recent species conditioning the soil and the plant species conditioning the soil before that. Thus it is the particular sequence of plant species that conditioned the soil before which determines current plant performance (Wubs & Bezemer 2018 Oikos). The fact that plant-soil feedback effects can carry-over like this has not been incorporated in mathematical models of plant-soil interactions and is potentially important to consider when optimizing sequences of plants in crop rotations.