Climate change effects in a semiarid grassland: Physiological responses to shifts in rain patterns

Guevara, Mónica Ladrón de; Lázaro, Roberto; Arnau-Rosalén, Eva; Domingo, Francisco; Molina-Sanchis, Isabel; Mora, J. L.

doi:10.1016/j.actao.2015.08.001

Cited by 8 publications

(7 citation statements)

References 47 publications

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“…However, in monoculture stands like our pots, higher WUE for C 4 grasses confers soil water savings, allowing stomata to remain open and extending the duration of assimilation. This has been shown in comparative analyses, in which declines in A were slower for C 4 than C 3 plants, particularly during the initial stages (2-3 weeks) of drought (Schulze and Hall, 1982;Ripley et al, 2010;Taylor et al, 2014), and is a recognized advantage under fluctuating water availability (Morgan et al, 2011;Ladrón de Guevara et al, 2015;Nie et al, 2018). Conversely, if soil water is shared between C 3 and C 4 plants, such as in mixed stands where the majority of tree and grass roots occupy upper soil layers (February and Higgins, 2010) and compete primarily for the same resources (Scholes and Archer, 1997), soils are likely to be wetter on average than in C 3 -only stands, providing a window of opportunity for C 3 grasses and trees to colonize stands of C 4 grasses.…”

Section: Stained Sapwoodmentioning

confidence: 78%

Response of photosynthesis, growth and water relations of a savannah-adapted tree and grass grown across high to low CO2

et al. 2019

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Background and Aims By the year 2100, atmospheric CO2 concentration ([CO2]a) could reach 800 ppm, having risen from ~200 ppm since the Neogene, beginning ~24 Myr ago. Changing [CO2]a affects plant carbon–water balance, with implications for growth, drought tolerance and vegetation shifts. The evolution of C4 photosynthesis improved plant hydraulic function under low [CO2]a and preluded the establishment of savannahs, characterized by rapid transitions between open C4-dominated grassland with scattered trees and closed forest. Understanding directional vegetation trends in response to environmental change will require modelling. But models are often parameterized with characteristics observed in plants under current climatic conditions, necessitating experimental quantification of the mechanistic underpinnings of plant acclimation to [CO2]a. Methods We measured growth, photosynthesis and plant–water relations, within wetting–drying cycles, of a C3 tree (Vachellia karroo, an acacia) and a C4 grass (Eragrostis curvula) grown at 200, 400 or 800 ppm [CO2]a. We investigated the mechanistic linkages between trait responses to [CO2]a under moderate soil drying, and photosynthetic characteristics. Key results For V. karroo, higher [CO2]a increased assimilation, foliar carbon:nitrogen, biomass and leaf starch, but decreased stomatal conductance and root starch. For Eragrostis, higher [CO2]a decreased C:N, did not affect assimilation, biomass or starch, and markedly decreased stomatal conductance. Together, this meant that C4 advantages in efficient water-use over the tree were maintained with rising [CO2]a. Conclusions Acacia and Eragrostis acclimated differently to [CO2]a, with implications for their respective responses to water limitation and environmental change. Our findings question the carbon-centric focus on factors limiting assimilation with changing [CO2]a, how they are predicted and their role in determining productivity. We emphasize the continuing importance of water-conserving strategies in the assimilation response of savannah plants to rising [CO2]a.

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Section: Stained Sapwoodmentioning

confidence: 78%

Response of photosynthesis, growth and water relations of a savannah-adapted tree and grass grown across high to low CO2

et al. 2019

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“…The photosynthetic behaviour of this species, measured as the green fraction of AGB within the canopy, also changes during the year and with landscape position in response to water availability. In fact, in the southeast of Spain, M. tenacissima L. has a growing or active period during late autumn and winter, while it remains in a latent state during spring and summer [101], leading to seasonal changes in GB that control ecosystem processes such as overall CO 2 dynamics [102]. Different studies describe good relationships between vegetation indices that represent the amount of photosynthetically active radiation such as NDVI and the GB amount [20,27,[102][103][104] and dynamics [17,18,28].…”

Section: Discussionmentioning

confidence: 99%

“…In fact, in the southeast of Spain, M. tenacissima L. has a growing or active period during late autumn and winter, while it remains in a latent state during spring and summer [101], leading to seasonal changes in GB that control ecosystem processes such as overall CO 2 dynamics [102]. Different studies describe good relationships between vegetation indices that represent the amount of photosynthetically active radiation such as NDVI and the GB amount [20,27,[102][103][104] and dynamics [17,18,28]. However, our results demonstrate that M. tenacissima L. GB shows weak relationships with all the vegetation indices tested at the plant scale (Table 4).…”

Section: Discussionmentioning

confidence: 99%

Non-Destructive Biomass Estimation in Mediterranean Alpha Steppes: Improving Traditional Methods for Measuring Dry and Green Fractions by Combining Proximal Remote Sensing Tools

et al. 2021

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The Mediterranean region is experiencing a stronger warming effect than other regions, which has generated a cascade of negative impacts on productivity, biodiversity, and stability of the ecosystem. To monitor ecosystem status and dynamics, aboveground biomass (AGB) is a good indicator, being a surrogate of many ecosystem functions and services and one of the main terrestrial carbon pools. Thus, accurate methodologies for AGB estimation are needed. This has been traditionally done by performing direct field measurements. However, field-based methods, such as biomass harvesting, are destructive, expensive, and time consuming and only provide punctual information, not being appropriate for large scale applications. Here, we propose a new non-destructive methodology for monitoring the spatiotemporal dynamics of AGB and green biomass (GB) of M. tenacissima L. plants by combining structural information obtained from terrestrial laser scanner (TLS) point clouds and spectral information. Our results demonstrate that the three volume measurement methods derived from the TLS point clouds tested (3D convex hull, voxel, and raster surface models) improved the results obtained by traditional field-based measurements. (Adjust-R2 = 0.86–0.84 and RMSE = 927.3–960.2 g for AGB in OLS regressions and Adjust-R2 = 0.93 and RMSE = 376.6–385.1 g for AGB in gradient boosting regression). Among the approaches, the voxel model at 5 cm of spatial resolution provided the best results; however, differences with the 3D convex hull and raster surface-based models were very small. We also found that by combining TLS AGB estimations with spectral information, green and dry biomass fraction can be accurately measured (Adjust-R2 = 0.65–0.56 and RMSE = 149.96–166.87 g in OLS regressions and Adjust-R2 = 0.96–0.97 and RMSE = 46.1–49.8 g in gradient boosting regression), which is critical in heterogeneous Mediterranean ecosystems in which AGB largely varies in response to climatic fluctuations. Thus, our results represent important progress for the measurement of M. tenacissima L. biomass and dynamics, providing a promising tool for calibration and validation of further studies aimed at developing new methodologies for AGB estimation at ecosystem regional scales.

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“…We suggest that C 4 grasses are not more competitive than trees under low water availability per se; instead, the interplay between the timing and duration of A , and the capacity to exploit soil water is critical. The ability of C 4 grasses to revert quickly from low to high A in response to precipitation inputs to soils would underpin higher time‐integrated assimilation and seasonal growth (Bellasio et al, ; Ladrón de Guevara et al, ) and potentially minimise metabolic impairment (Ripley et al, ). Conversely, lower A and slower stomatal responses to water inputs would disadvantage trees under low [CO 2 ] a , making them more vulnerable to grass‐fuelled fires, suppressing recruitment from saplings to trees (Bond, ; Staver et al, ).…”

Section: Discussionmentioning

confidence: 99%

C₄ savanna grasses fail to maintain assimilation in drying soil under low CO₂ compared with C₃ trees despite lower leaf water demand

et al. 2018

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C4 photosynthesis evolved when grasses migrated out of contracting forests under a declining atmospheric CO2 concentration ([CO2]a) and drying climate around 30 million years ago. C4 grasses are hypothesised to benefit from improved plant–water relations in open habitats such as savannas, giving advantages over C3 plants under low [CO2]a. But experimental evidence in a low CO2 environment is limited, and comparisons with C3 trees are needed to understand savanna vegetation patterns. To test whether stomatal conductance (gS) and CO2 assimilation (A) are maintained in drier soil for C4 grasses than C3 trees, particularly under low [CO2]a, we investigated photosynthesis and plant–water relations of three C3 tree and three C4 grass species grown at 800, 400 or 200 ppm [CO2]a over moderate wetting–drying cycles. C4 grasses had a lower soil‐to‐leaf water potential gradient than C3 trees, especially at 200 ppm [CO2]a, indicating reduced leaf water demand relative to supply. Yet the dependence of gS and A on predawn leaf water potential (a measure of soil water availability) was greater for the C4 grasses than trees, particularly under low [CO2]a. Our findings establish that gS and A are not maintained in drier soil for C4 grasses compared with C3 trees, suggesting that this mechanism was not prevailing in the expansion of C4‐dominated grasslands under low [CO2]a. This inherent susceptibility to sudden decreases in soil water availability justifies why C4 grasses have not evolved a resistant xylem allowing operation under drought, but instead shut down below a water potential threshold and rapidly recover. We point to this capacity to respond to transient water availability as a key overlooked driver of C4 grass success under low [CO2]a. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13240/suppinfo is available for this article.

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Climate change effects in a semiarid grassland: Physiological responses to shifts in rain patterns

Cited by 8 publications

References 47 publications

Response of photosynthesis, growth and water relations of a savannah-adapted tree and grass grown across high to low CO2

Response of photosynthesis, growth and water relations of a savannah-adapted tree and grass grown across high to low CO2

Non-Destructive Biomass Estimation in Mediterranean Alpha Steppes: Improving Traditional Methods for Measuring Dry and Green Fractions by Combining Proximal Remote Sensing Tools

C₄ savanna grasses fail to maintain assimilation in drying soil under low CO₂ compared with C₃ trees despite lower leaf water demand

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Climate change effects in a semiarid grassland: Physiological responses to shifts in rain patterns

Cited by 8 publications

References 47 publications

Response of photosynthesis, growth and water relations of a savannah-adapted tree and grass grown across high to low CO2

Response of photosynthesis, growth and water relations of a savannah-adapted tree and grass grown across high to low CO2

Non-Destructive Biomass Estimation in Mediterranean Alpha Steppes: Improving Traditional Methods for Measuring Dry and Green Fractions by Combining Proximal Remote Sensing Tools

C4 savanna grasses fail to maintain assimilation in drying soil under low CO2 compared with C3 trees despite lower leaf water demand

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C₄ savanna grasses fail to maintain assimilation in drying soil under low CO₂ compared with C₃ trees despite lower leaf water demand