Research Collection Doctoral Thesis Effects of nitrogen-addition and irrigation on the structure and function of ectomycorrhizal communities Author(s): Hutter, Sylvia Christa Publication Date: 2014 Permanent Link: https://doi.org/10.3929/ethz-a-010140121 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library DISS. ETH Nr. 21469 EFFECTS OF NITROGEN-ADDITION AND IRRIGATION ON THE STRUCTURE AND FUNCTION OF ECTOMYCORRHIZAL COMMUNITIES Abhandlung zur Erlangung des Titels DOKTORIN DER WISSENSCHAFTEN der ETH ZÜRICH (Dr. sc. ETH Zürich) vorgelegt von SYLVIA CHRISTA HUTTER Mag. rer. nat., Karl-Franzens-Universität geboren am 03.04.1981 österreichische Staatsbürgerin angenommen auf Antrag von Prof. Markus Aebi, Referent Dr. Martina Peter, Korreferentin Dr. Jean Garbaye, Korreferent Prof. Rosmarie Honegger, Korreferentin 2014 Table of contents Summary 2 Zusammenfassung 7 General Introduction 13 Chapter 1 30 Enzyme activities show a stronger dependency on ectomycorrhizal fungal morphotypes than on long-term nitrogen-addition and season in a spruce forest Chapter 2 71 The ectomycorrhizal fungal community of a drought-stressed Scots pine forest is functionally resilient to irrigation General Discussion and Conclusion 112 Danksagung 122 1 Summary Ectomycorrhizal (ECM) fungi live in symbiosis with most temperate forest trees. In this partnership, the fungus increases the water and nutrient uptake of the tree and in return receives sugars from the plant. Due to environmental factors such as nitrogen deposition, drought periods or season fungal communities can change their structure, including the community composition, the species richness, and the abundance of individual ECM species. Little is known, however, about both the functional response of these fungi to environmental impacts, and about the distribution of the function of ECM morphotypes within their communities. Relevant functional traits include for instance the activities of extracellular enzymes involved in the nutrient acquisition from organic matter. In this doctoral thesis the following questions were investigated: Do factors such as long-term nitrogen addition in a spruce forest, irrigation in a dry pine forest and seasons such as spring and autumn change the structure of ECM communities? Do the functional abilities of the ECM morphotypes and the communities differ when tested through enzyme activities? If the functional abilities differ, can we relate any pattern of the functional profile or functional plasticity of the ECM morphotypes to their abundance reaction due to the factors? The environmental factors fertilization, drought and spring may facilitate a reduction in the carbon flow from the tree to the fungus. Due to fertilization sufficient inorganic nutrients, particularly nitrogen, are available, which may cause the trees to limit the carbon allocation to their partnering fungi. Drought leads to a decrease in photosynthesis, resulting in a scarcity of sugars produced by trees, which 2 subsequently might reduce the carbon flow to the fungi. Similarly, because sugar reserves are needed for building new biomass and the available sunlight is insufficient for maximum sugar production by photosynthesis in spring, trees may pass on less sugar to their partnering fungi during this season. From these arguments, three hypotheses can be put forward in general. First, we expected that fungi that have a high ability to degrade organic carbon, and can therefore supply themselves with carbon, are favoured in environments where carbon supply from trees is limited. This implies that a higher abundance of such species should be observed in fertilized plots, during drought periods and in spring. Second, for ECM fungi which show no abundance changes in response to these factors, a high ability for adaptation reflected by plastic enzyme activities might be present. Third, carbon limitation might favour ECM fungi that are less carbon demanding because they produce comparatively little external mycelium such as the so-called contact or short- distance exploration types. Specifically for the response of ECM fungi to fertilization, we can put forward two further hypotheses. First, fungi that possess a high ability to degrade organic nitrogen can be expected to show reduced abundances in fertilized plots. Their special ability would not be advantageous in an environment with high availability of inorganic nitrogen. Second, fungi that show increased abundances in the nitrogen-addition plots are expected to be competent in degrading organic phosphate, since this element is likely to be a limiting growth factor in such an environment. Specifically for the response of ECM fungi to drought, an additional hypothesis can be stated. Enzyme activities for phosphate and nitrogen mobilization can be expected to be higher in ECM fungi favouring dry conditions compared to other fungi, since a higher nutrient status enhances drought tolerance. 3 We tested these hypotheses in two experiments. Chapter one deals with a long-term high nitrogen deposition experiment, which was simulated in a Swiss spruce forest by fertilizing 150 kg nitrogen ha-1a-1. In chapter two an irrigation experiment is described, which was carried out in a pine dominated forest in one of the driest valleys in Switzerland. In both experiments, the ECM communities were investigated by visual classification, by ITS sequencing, and by counting of ECM root tips. The functional response was determined by measuring activities of enzymes involved in organic matter degradation. The measurements were performed four times in two seasons (spring 2008 and 2009, autumn 2007 and 2008). The ECM communities changed drastically in response to nitrogen addition and moderately in response to irrigation and season. All three factors (nitrogen addition, irrigation and season) affected the relative abundances of ECM morphotypes. Moreover, the number of ECM root tips and the species diversity declined after nitrogen addition. During spring, the species richness increased compared to autumn in the irrigation experiment, whereas irrigation did not lead to a change in diversity. In both studies, enzyme activities per mm2 of the ECM communities differed to a little degree between treatment and control plots. Small but significant increases were observed for sugar degrading enzymes due to nitrogen addition and in the dry controls of the irrigation study. The phosphatase increased its activity due to spring compared to autumn in the nitrogen-addition study and increased in the dry controls of the irrigation experiment. Moreover, leucine aminopeptidase, responsible for protein degradation, increased in spring compared to autumn in both studies. Total enzyme activities of the ECM communities cumulated over all ECM root tips were drastically reduced after nitrogen addition because the number of ECM root tips was 4 reduced by more than half compared to the control plots. No significant change was observed in the total enzyme activities in the irrigation experiment. All ECM morphotypes were able to produce all of the investigated enzymes, but the measured values differed for each morphotype. However, no simple relation was found between the enzyme activities and the abundance reactions of the ECM morphotypes due to the investigated factors. Within individual ECM morphotypes, several significant differences of enzyme activities were observed due to nitrogen addition, irrigation and season. In the nitrogen-addition experiment, enzyme activities mostly increased due to nitrogen addition and spring. In the irrigation study, enzyme activities were higher in the dry controls compared to irrigated plots and again in spring compared to autumn. Our results over both studies indicate that the functional traits of the ECM communities were maintained, although a shift in the ECM fungal composition was observed to a high degree in the nitrogen-addition study and to a moderate degree in the irrigation study and due to season. This suggests redundant functional abilities among ECM morphotypes and therefore can be interpreted as a resilient reaction of these ecosystems. However, since the number of ECM root tips was drastically reduced due to nitrogen-addition, the total enzyme activities were diminished, which might influence the nutrient cycles in this ecosystem. This was already reflected as reduced concentrations of several elements such as phosphate in the needles of the nitrogen-addition trees. In the irrigation study no change in total enzyme activities was observed. This functional and structural intact ECM community in the drought- stressed ecosystem might have facilitated the previously observed fast recovery of drought stressed Scots pine trees. Several ECM morphotypes with abundance changes and stable abundances exhibited a high degree of adaptation in their functional traits. The results do not 5 agree with the hypothesis that ECM morphotypes showing stable abundance exhibit a high degree of plasticity for adapting to changing conditions. In contrast, ECM morphotypes with changes in abundance are also able to adapt to varying conditions. In the present studies, most of the ECM morphotypes did not show the expected patterns in their enzyme activities related to their changed abundances, which could be explained by a reduced carbon supply as in our hypotheses. Therefore, other factors seem to be more important