Unperturbed root fungal communities in a temperate forest recovering from five years of reoccurring droughts

<p>Since industrialization, the global average temperature increases with far reaching consequences for the world climate. One phenomenon is the current occurrence of more heavy and long droughts in Middle Europe, which lead to extensive tree die-off and shows that we need a better understanding of the forest-soil ecosystem in times of climate change.</p><p>Within the interdisciplinary Kranzberg Roof Experiment, we study the drought resistance and drought recovery of mature Norway spruce (<em>Picea abies</em>) and European beech (<em>Fagus sylvatica</em>). The trees experienced a rainfall exclusion for five years during the vegetation period and were rewetted by drip irrigation in summer 2019. Our interest focuses in the functional role of ectomycorrhizal and overall fungal communities on tree drought resistance and recovery. Particularly, we hypothesized the rewetting event will lead to a shift in community structure because of steeply rising water and nutrient availabilities.</p><p>To get insights to the development of the fungal communities right after the rewetting period, we sequenced the fungal ITS2 region of fine root DNA extracts. The roots were taken from soil cores before and at several time-points after irrigation.</p><p>We found that the fungal communities stayed quite similar to each other during the time-frame of recovery we investigated (84 days), while the amount of new root tips strongly increased directly after the rewetting. Surprisingly, the organic material which had accumulated as it was not degraded during the years of drought, did not lead to a shift in community composition. In particular, there were no changes in the relative amounts of saprotroph fungi in the phase after the rewetting.</p><p>Therefore, root fungal communities – the interface between trees and soil – seemingly did not experience a strong pressure to adapt their composition to the new condition, which matches their resistant behavior during the long drought phase before (cf. abstract 2937).</p>

Are ectomycorrhizal fungi actually adapting to 5 years of extreme summer drought in Middle European forests?

<p>Middle Europe’s forests face an increasing risk of recurring summer droughts. To explore the impact of such conditions, trees in a mature spruce-beech forest were exposed to five successive years of extreme summer drought during the Kranzberg Roof Experiment located in Bavaria (Grams et al. 2021, DOI: 10.1002/ecs2.3399).</p><p>Those trees (<em>Picea abies</em> and <em>Fagus sylvatica</em>) heavily depend on their ectomycorrhizal fungal symbiosis partners (ECMf) belowground. Thus, we set out to identify modes of compositional and functional adaptation in these communities.</p><p>We monitored ECMf communities via metabarcoding and analysed the functionality of morphotyped ectomycorrhizae via testing their enzyme activities.</p><p>To our surprise, most effects were quantitative throughout the whole period. Total enzyme activities strongly declined alongside the numbers of vital root tips of drought treated trees, while enzyme activities per surviving root tip remained remarkably similar to controls. Likewise, ECMf communities only experienced minor shifts that only slightly increased during the years, although different capacities for drought tolerance in ECMf have previously been hypothesised.</p><p>Summed up: Along with most tree individuals, their fungal partners showed a strong ability to resist the applied extreme drought scenario, at the cost of severely diminished capacities at the ecosystems level.</p><p>Speculatively, individual root tips could be seen as surviving insulae whose fungal communities only experienced indirect and moderated drought effects. Therefore, the ECM system may rather show an inherent resistance to drought, with observable qualitative adaptation requiring a still longer time-frame.</p>

Five years of experimental summer drought – Anatomical and physiological acclimation of mature beech and spruce

<p>This contribution summarizes the outcome of a five-year experiment on mature (60-80 years old) trees in a Central European forest. We studied roughly 100 trees of European beech and Norway spruce, two tree species of contrasting foliage (i.e. deciduous vs. evergreen) and stomatal sensitivity to drought (i.e. anisohydric vs. isohydric behavior). Trees were exposed to experimentally induced summer droughts from 2014 to 2018 with precipitation throughfall being completely excluded during the growing seasons. The throughfall-exclusion study was established on 12 plots with trees readily accessible by canopy crane (Kranzberg forest roof experiment, southern Germany). We aimed at bringing trees to the edge of survival to studying trees’ capability for acclimation under repeated, severe summer droughts as expected more frequently in future climate scenarios. Results come from a multidisciplinary approach focusing on mechanisms of acclimation, eventually reducing trees’ vulnerability to drought during the five-year study period. Presented data integrate responses from the level of soil/microbial interactions over tree organs and whole-tree morphology to responses at the stand level.</p><p>During the first two years, restrictions caused by drought were most prominent, exemplified by pre-dawn leaf water potentials of down to -2.5 MPa and reductions in photosynthesis and growth by up to 50 and 80 % in European beech and Norway spruce, respectively. Nevertheless, percentage loss of conductivity in branch xylem was hardly affected. Likewise, concentrations of non-structural carbohydrates (sum of soluble sugars and starch) in tree organs remained largely unaffected, but translated to significantly lower carbohydrate pool sizes in view of strongly reduced tree growth. Nevertheless, two spruce trees died from drought, in the absence of bark beetle or pathogen interactions. During the fourth and fifth year of summer drought, trees showed clear signs of drought acclimation with e.g. some recovery of stomatal conductance, reductions of whole-tree leaf area, changes in rooting depth and acclimation of associated soil microbial communities. Accordingly, stem diameter growth recovered during the last years of the stress treatment, indicating reduced vulnerability of trees towards the end of the five-year drought treatment.</p>

Spruce resins constitute a strong sink for methane (CH4)

<p>Woody plants are known to emit methane (CH<sub>4</sub>) as an important greenhouse gas into the atmosphere. Recent studies show that tree stems might be also sinks for CH<sub>4</sub>; however, the mechanisms of CH<sub>4</sub> uptake and its fate are unknown. Norway spruce (<em>Picea abies)</em> is characterised as negligible CH<sub>4 </sub>source in boreal forests. Even though spruce trees have been widely planted for its wood in large-scale monocultures in European temperate forests, no studies have focused on their CH<sub>4</sub> exchange potential in the temperate zone.</p><p>We determined stems of Norway spruce growing in a temperate zone aiming to find out whether the tree stems exchange CH<sub>4</sub> with the atmosphere and how they contribute to the forest trace gas exchange.</p><p>The measurements were performed at the experimental station of the ‘Kranzberg Forest Roof Experiment’ near Freising, Germany, in June 2019. Fluxes of CH<sub>4</sub> in mature tree stems were measured using non-steady-state stem chamber systems (n=32) installed in stem vertical profile approx. two weeks prior to measurements using a portable greenhouse gas analyser. Moreover, resins sampled from spruce stems were investigated for their CH<sub>4</sub> exchange potential. Control measurements were performed to ensure that the fluxes do not originate from used chamber materials, in particular silicones used for chamber installation.</p><p>Our preliminary results show that the spruce stems can be a strong sink for CH<sub>4</sub> (-0.288 ± 0.053 mg CH<sub>4</sub> m<sup>-2</sup> stem area h<sup>-1</sup>, mean ± s.e.), even if a small amount of resin is present on the bark. The stems exuded resins to different extent (covering 4.8 ± 1.3% of the stem surface area in chambers), partly as a result of smoothening of rough surface layers of dead bark for chamber installation. However, even spruce stems without obvious “injuries” released small amounts of resins for unknown reasons (response to drought, bark-beetle attack, etc.?). The incubated resin samples consistently consumed CH<sub>4</sub> (-12.0 ± 1.7 mg CH<sub>4</sub> m<sup>-2</sup> resin area h<sup>-1</sup>). Moreover, the detected stem CH<sub>4</sub> uptake negatively correlated with the resin occurrence in the stem chambers (R² = 0.884). After re-calculation of the stem fluxes to resin area, the CH<sub>4</sub> consumption rates of stems and resin samples were in the same order of magnitude at median level (-13.2 and -12.0 mg CH<sub>4</sub> m<sup>-2</sup> resin area h<sup>-1</sup>, resp.).</p><p>Concluded, the spruce resins appear to be a very strong and until now undiscovered sink for CH<sub>4</sub>. Even one small droplet of resins on bark can turn the known negligible CH<sub>4</sub> exchange of intact spruce stems into strong CH<sub>4</sub> sinks, having thus severe impact on the overall forest CH<sub>4</sub> balance. This consumption potential of fresh resins should be considered by estimation of forest ecosystem CH<sub>4</sub> balance especially in areas, where resin bleeding is widely spread or is to be expected (bark-beetle areas, drought events, tree harvest, clear-cutting).</p><p> </p><p><em>Acknowledgement</em></p><p><em>This research was supported by the Czech Science Foundation (17-18112Y) and National Sustainability Program I (LO1415). We thank Prof. Thorsten Grams for all his kind support, and Jan Hrdlička and Thomas Feuerbach for their technical support.</em></p><p> </p><p> </p>

Stormwater Retention and Reuse at the Residential Plot Level—Green Roof Experiment and Water Balance Computations for Long-Term Use in Cyprus

Green roofs can provide various benefits to urban areas, including stormwater retention. However, semi-arid regions are a challenging environment for green roofs as long dry weather periods are met with short but intense rainfall events. This requires green roofs to retain maximum volumes of stormwater, while being tolerant to minimal irrigation supplies. The objectives of this study are (i) to quantify the stormwater retention of two substrate mixtures with two plant species under natural rainfall; (ii) to assess the performance of two plant species under two levels of deficit irrigation; and (iii) to compute stormwater runoff reduction and reuse by green roofs and rooftop water harvesting systems for three standard residential plot types in urban Nicosia, Cyprus. A rooftop experiment was carried out between February 2016 and April 2017 and results were used to compute long-term performance. Average stormwater retention of the 16 test beds was 77% of the 371-mm rainfall. A survival rate of 88% was recorded for Euphorbia veneris and 20% for Frankenia laevis, for a 30% evapotranspiration irrigation treatment. A combination of a green roof, rainwater harvesting system and 20-m3 tank for irrigation and indoor greywater use reduced stormwater runoff by 47–53%, for the 30-year water balance computations.

Performance analysis and experimental study on rainfall water purification with an extensive green roof matrix layer in Shanghai, China

Current research has validated the purification of rainwater by a substrate layer of green roofs to some extent, though the effects of the substrate layer on rainwater purification have not been adequately quantified. The present study set up nine extensive green roof experiment combinations based on the current conditions of precipitation characteristics observed in Shanghai, China. Different rain with pollutants were simulated, and the orthogonal design L9 (33) test was conducted to measure purification performance. The purification influences of the extensive green roof substrate layer were quantitatively analyzed in Shanghai to optimize the thickness, proportion of substrate, and sodium polyacrylate content. The experimental outcomes resulted in ammonium nitrogen (NH4+-N), lead (Pb), and zinc (Zn) removal of up to 93.87%, 98.81%, and 94.55% in the artificial rainfall, respectively, and NH4+-N, Pb, and Zn event mean concentration (EMC) was depressed to 0.263 mg/L, 0.002 mg/L and 0.018 mg/L, respectively, which were all well below the pollutant concentrations of artificial rainfall. With reference to the rainfall chemical characteristics of Shanghai, a combination of a 200 mm thickness, proportions of 1:1:2 of Loam: Perlite: Cocopeat and 2 g/L sodium polyacrylate content was suggested for the design of an extensive green roof substrate to purify NH4+-N, Pb and Zn.