Separating continuously measured stem radius (SR) fluctuations into growth-induced irreversible stem expansion (GRO) and tree water deficit-induced reversible stem shrinkage (TWD) requires a ...conceptualization of potential growth processes that may occur during periods of shrinking and expanding SR below a precedent maximum. Here, we investigated two physiological concepts: the linear growth (LG) concept, assuming linear growth, versus the zero growth (ZG) concept, assuming no growth during periods of stem shrinkage.
We evaluated the physiological mechanisms underlying these two concepts and assessed their respective plausibilities using SR data obtained from 15 deciduous and evergreen trees.
The application of the LG concept produced steady growth rates, whereas growth rates varied strongly under the ZG concept, more in accordance with mechanistic expectations. Further, growth increased for a maximum of 120 min after periods of stem shrinkage, indicating limited growth activity during those periods. However, this extra growth was found to be a small fraction of total growth only. Furthermore, TWD under the ZG concept was better explained by a hydraulic plant model than TWD under the LG concept.
We conclude that periods of stem shrinkage allow for very little growth in the four tree species investigated. However, further studies should focus on obtaining independent growth data to ultimately validate these findings.
We assessed how the seasonal variability of precipitation δ2H and δ18O is propagated into soil and xylem waters of temperate trees, applied a hydrological model to estimate the residence time ...distribution of precipitation in the soil, and identified the temporal origin of water taken up by Picea abies and Fagus sylvatica over 4 yr.
Residence times of precipitation in the soil varied between a few days and several months and increased with soil depth. On average, 50% of water consumed by trees throughout a year had precipitated during the growing season, while 40% had precipitated in the preceding winter or even earlier. Importantly, we detected subtle differences with respect to the temporal origin of water used by the two species.
We conclude that both current precipitation and winter precipitation are important for the water supply of temperate trees and that winter precipitation could buffer negative impacts of spring or summer droughts.
Our study additionally provides the means to obtain realistic estimates of source water δ2H and δ18O values for trees from precipitation isotope data, which is essential for improving model-based interpretations of δ18O and δ2H values in plants.
Legumes are different Adams, Mark Andrew; Turnbull, Tarryn L.; Sprent, Janet I. ...
Proceedings of the National Academy of Sciences,
04/2016, Letnik:
113, Številka:
15
Journal Article
Recenzirano
Odprti dostop
Using robust, pairwise comparisons and a global dataset, we show that nitrogen concentration per unit leaf mass for nitrogen-fixing plants (N₂FP; mainly legumes plus some actinorhizal species) in ...nonagricultural ecosystems is universally greater (43–100%) than that for other plants (OP). This difference is maintained across Koppen climate zones and growth forms and strongest in the wet tropics and within deciduous angiosperms. N₂FP mostly show a similar advantage over OP in nitrogen per leaf area (Narea), even in arid climates, despite diazotrophy being sensitive to drought. We also show that, for most N₂FP, carbon fixation by photosynthesis (Asat) and stomatal conductance (gs) are not related to Narea—in distinct challenge to current theories that place the leaf nitrogen–Asat relationship at the center of explanations of plant fitness and competitive ability. Among N₂FP, only forbs displayed an Narea–gs relationship similar to that for OP, whereas intrinsic water use efficiency (WUEi; Asat/gs) was positively related to Narea for woody N₂FP. Enhanced foliar nitrogen (relative to OP) contributes strongly to other evolutionarily advantageous attributes of legumes, such as seed nitrogen and herbivore defense. These alternate explanations of clear differences in leaf N between N₂FP and OP have significant implications (e.g., for global models of carbon fluxes based on relationships between leaf N and Asat). Combined, greater WUE and leaf nitrogen—in a variety of forms—enhance fitness and survival of genomes of N₂FP, particularly in arid and semiarid climates.
Why trees grow at night Zweifel, Roman; Sterck, Frank; Braun, Sabine ...
The New phytologist,
September 2021, Letnik:
231, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Summary
The timing of diel stem growth of mature forest trees is still largely unknown, as empirical data with high temporal resolution have not been available so far. Consequently, the effects of ...day–night conditions on tree growth remained uncertain.
Here we present the first comprehensive field study of hourly‐resolved radial stem growth of seven temperate tree species, based on 57 million underlying data points over a period of up to 8 yr.
We show that trees grow mainly at night, with a peak after midnight, when the vapour pressure deficit (VPD) is among the lowest. A high VPD strictly limits radial stem growth and allows little growth during daylight hours, except in the early morning. Surprisingly, trees also grow in moderately dry soil when the VPD is low. Species‐specific differences in diel growth dynamics show that species able to grow earlier during the night are associated with the highest number of hours with growth per year and the largest annual growth increment.
We conclude that species with the ability to overcome daily water deficits faster have greater growth potential. Furthermore, we conclude that growth is more sensitive than carbon uptake to dry air, as growth stops before stomata are known to close.
Over the last decade, it has been shown in the ecology literature that species diversity increases yield stability in managed grasslands. Here, we develop and apply ecological economic and ...econometric frameworks to evaluate these potential risk-reducing effects of species diversity in terms of yields and their temporal stability from a farmer's perspective. Our empirical analysis is based on a rich panel dataset obtained from a diversity experiment covering in total 60 species and a period of 6years. We find empirical evidence for the risk-reducing effect of species diversity and the economic assessment reveals significant insurance values associated with diversity for a risk-averse decision maker. Thus, the economic value of diversity would be underestimated if not accounting for this property, and species diversity may serve as valuable ex-ante risk management strategy.
•We use data from a rich diversity experiment covering in total 60 species and a period of 6years.•Species diversity has a risk-reducing effect on grassland yield.•For risk averse decision maker, species diversity has significant insurance values.•Diversity can serve as valuable ex-ante risk management strategy.
The response of soil respiration to varying environmental factors was studied in four
Picea abies stands (47-, 87-, 111- and 146-year old) during the 1998 growing season. While within-site variations ...of soil CO
2 efflux (up to 1.6 μmol CO
2 m
−2 s
−1) were larger than their diurnal variability (<0.25 μmol CO
2 m
−2 s
−1), spatial variations within a site were smaller than seasonal changes in soil respiration rates (up to 4.4 μmol CO
2 m
−2 s
−1). Highest within-site variability of soil efflux was generally found during the summer months when maximum flux rates of 4–6 μmol CO
2 m
−2 s
−1 were reached (coefficient of variation 40%). Soil temperatures (in the O
f and O
h layers, and A
h horizon) showed a pronounced seasonal course, in contrast to soil moisture. An exponential equation best described the relationships between soil temperature in the O
f layer and soil CO
2 efflux (
r
2 between 0.75 and 0.81). However, an Arrhenius type equation always resulted in lower
r
2 values (0.52–0.71). The
Q
10 values ranged between 2.39 (146-year old stand) and 3.22 (87-year old stand), averaging 2.72 for the
P. abies stands within the watershed. The removal of litter and organic layers generally affected soil CO
2 efflux negatively. In three of the four
P. abies stands (47-, 87-, 146-year old stands), soil respiration rates were reduced by 10–20% after removal of the L and O
f layer, and by 30–40% after removal of the L and most of the O
f and O
h layers. Thus, mineral soil respiration seemed to contribute a major fraction to the total soil CO
2 flux (>60%). Trenching shallow fine roots during collar insertion and mechanical inhibition of root in-growth during the following months allowed fine root respiration to be separated from microbial respiration only in times of highest root growth. Microbial respiration seemed to dominate the respiratory CO
2 loss from the forest floor (>70%). The comparison of the annual soil CO
2 efflux in the 47-year old
P. abies stand (about 710 g C m
−2 yr
−1) with annual litterfall and root net primary productivity estimates supported this conclusion.
In agricultural settings, plant diversity is often associated with low biomass yield and forage quality, while biodiversity experiments typically find the opposite. We address this controversy by ...assessing, over 1 year, plant diversity effects on biomass yield, forage quality (i.e. nutritive values), quality-adjusted yield (biomass yield × forage quality), and revenues across different management intensities (extensive to intensive) on subplots of a large-scale grassland biodiversity experiment. Plant diversity substantially increased quality-adjusted yield and revenues. These findings hold for a wide range of management intensities, i.e., fertilization levels and cutting frequencies, in semi-natural grasslands. Plant diversity was an important production factor independent of management intensity, as it enhanced quality-adjusted yield and revenues similarly to increasing fertilization and cutting frequency. Consequently, maintaining and reestablishing plant diversity could be a way to sustainably manage temperate grasslands.
Diffuse radiation generally increases photosynthetic rates if total radiation is kept constant. Different hypotheses have been proposed to explain this enhancement of photosynthesis, but conclusive ...results over a wide range of diffuse conditions or about the effect of canopy architecture are lacking. Here, we show the response of canopy photosynthesis to different fractions of diffuse light conditions for five major arable crops (pea, potato, wheat, barley, rapeseed) and cover crops characterized by different canopy architecture. We used 13 years of flux and microclimate measurements over a field with a typical 4 year crop rotation scheme in Switzerland. We investigated the effect of diffuse light on photosynthesis over a gradient of diffuse light fractions ranging from 100% diffuse (overcast sky) to 11% diffuse light (clear‐sky conditions). Gross primary productivity (GPP) increased with diffuse fraction and thus was greater under diffuse than direct light conditions if the absolute photon flux density per unit surface area was kept constant. Mean leaf tilt angle (MTA) and canopy height were found to be the best predictors of the diffuse versus direct radiation effect on photosynthesis. Climatic factors, such as the drought index and growing degree days (GDD), had a significant influence on initial quantum yield under direct but not diffuse light conditions, which depended primarily on MTA. The maximum photosynthetic rate at 2,000 µmol m−2 s−1 photosynthetically active radiation under direct conditions strongly depended on GDD, MTA, leaf area index (LAI) and the interaction between MTA and LAI, while under diffuse conditions, this parameter depended mostly on MTA and only to a minor extent on canopy height and their interaction. The strongest photosynthesis enhancement under diffuse light was found for wheat, barley and rapeseed, whereas the lowest was for pea. Thus, we suggest that measuring canopy architecture and diffuse radiation will greatly improve GPP estimates of global cropping systems.
Gross primary productivity increased with diffuse light fraction if the absolute photon flux density per unit surface area was kept constant. We investigated the effect of diffuse light on photosynthesis over a gradient of diffuse light fractions ranging from 100% diffuse (overcast sky) to 11% diffuse light (clear‐sky conditions) using 13 years of flux and microclimate measurements. Mean leaf tilt angle and canopy height were found to be the best predictors of the diffuse versus direct radiation effect on photosynthesis. The strongest photosynthesis enhancement was found for wheat, barley and rapeseed, the lowest was for pea.
Due to the large carbon dioxide (CO2) fluxes between terrestrial ecosystems and the atmosphere, dynamics of photosynthesis can have significant effects on atmospheric CO2 concentrations and lead to ...large uncertainties in ecosystem C budgets. Remote sensing approaches using sun-induced chlorophyll fluorescence (SIF) hold the potential to directly assess ecosystem photosynthesis. However, many challenges remain linked to using the SIF emission signal to estimate gross primary production (GPP). The goal of this study was to gain a better understanding of the relationships between GPP and SIF over different time scales (minutes to years) and under varying environmental conditions. Two different ecosystems were investigated, a cropland and a mixed forest, with continuous eddy covariance flux measurements. Continuous tower-based SIF retrievals were performed in 2015 and 2016 at both ecosystems.
In both ecosystems, SIF was found to be more affected by environmental conditions than GPP. Annual cycles for GPP and SIF differed at the mixed forest due in part to the influence of the different footprint size of the two independent measurements. Diurnal cycles in GPP and SIF corresponded well under unstressed conditions and followed the incoming photosynthetic photon flux density (PPFD). However, depressions in SIF were found at both sites either at midday or in the afternoon during the growing season. At the cropland site, reductions in SIF occurred at high PPFD (PPFD > 1470 μmol m−2 s−1, R2 = 0.62) and high VPD (VPD > 1590 Pa, R2 = 0.35). Whereas at the forest site, reductions in SIF were linked to high VPD (VPD > 1250 Pa, R2 = 0.25), but not to high PPFD (R2 = 0.84). The depression in SIF was also associated with an increase in non-photochemical quenching, as indicated by the photochemical reflectance index (R2 = 0.78), thus showing the complementarity between SIF and non-photochemical quenching as different energy pathways. Our results show the importance of characterizing the influence of different environmental conditions on SIF-GPP relationships for specific ecosystems to reliably estimate GPP from remote sensing measurements.
•A continuous time-series of tower-based sun-induced fluorescence was measured.•SIF and GPP had similar annual and diurnal patterns.•Depressions in SIF were found under high light and/or high VPD conditions.•Environmental conditions affect the ecosystem derived SIF-GPP relationships.
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