The importance of extreme rainfall events and their timing in a semi‐arid grassland

Post, Alison K.; Knapp, Alan K.

doi:10.1111/1365-2745.13478

Cited by 65 publications

(62 citation statements)

References 103 publications

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“…Roofs were installed 1 m above ground‐level and angled slightly to direct water drainage away from the plots. Previous research indicates that the shelters only moderately reduce transmission of photosynthetically active radiation (PAR; average reduction of 16.4 ± 5.4%, Post & Knapp, 2020) and have minimal effects on the microclimate and plant responses (Loik et al, 2019).…”

Section: Methodsmentioning

confidence: 99%

“…The deluge treatments included the addition of a single rain event that was either 20, 40, 60, 80, 100, or 120 mm in size. Deluges were added in the midgrowing season (Jul 10–12) when the shortgrass steppe is highly responsive to large water inputs (Post & Knapp, 2020). Our goal was to include deluge sizes representing large rain events that occur relatively frequently in this ecosystem (20 mm), as well as historically unprecedented deluges that might occur in the future as the climate changes (120 mm).…”

Section: Methodsmentioning

confidence: 99%

“…At the end of the growing season, we assessed above‐ and belowground net primary production (ANPP, BNPP). Methods generally followed protocols in Post and Knapp (2020).…”

Section: Methodsmentioning

confidence: 99%

“…Soil volumetric water content (VWC) was measured at the plot center and integrated over the top 20 cm of soil using a time domain reflectometry (TDR) probe (Campbell Hydrosense II). Measurements were corrected for soil texture of the site using gravimetric soil moisture measurements (Post & Knapp, 2020). To monitor soil respiration, a permanent PVC collar (10 cm diameter) was installed in each plot at the beginning of the growing season to a depth of 2.4 cm and extending 2 cm aboveground.…”

Section: Methodsmentioning

confidence: 99%

“…Since they are water‐limited, arid and semiarid ecosystems exhibit a strong positive relationship between annual precipitation and aboveground net primary production (ANPP; Bai et al, 2008; Huxman, Smith, et al, 2004; Knapp & Smith, 2001; La Pierre et al, 2016; Lauenroth & Sala, 1992; Sala et al, 1988). Even a single deluge event can substantially increase annual rainfall in these dry systems (Knapp et al, 2015; Sala et al, 1992), and thus stimulate plant growth and impact other ecosystem processes (Guo et al, 2015; Heisler‐White et al, 2008; Lauenroth & Sala, 1992; Li et al, 2013; Post & Knapp, 2020). Typically, large rain events more effectively increase soil moisture than equivalent water inputs via multiple small rain events (Guo et al, 2015; Heisler‐White et al, 2008; Knapp et al, 2008; Zeppel et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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How big is big enough? Surprising responses of a semiarid grassland to increasing deluge size

Post

Knapp

2020

Global Change Biology

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Climate change has intensified the hydrologic cycle globally, increasing the magnitude and frequency of large precipitation events, or deluges. Dryland ecosystems are expected to be particularly responsive to increases in deluge size, as their ecological processes are largely dependent on distinct soil moisture pulses. To better understand how increasing deluge size will affect ecosystem function, we conducted a field experiment in a native semiarid shortgrass steppe (Colorado, USA). We quantified ecological responses to a range of deluge sizes, from moderate to extreme, with the goal of identifying response patterns and thresholds beyond which ecological processes would not increase further (saturate). Using a replicated regression approach, we imposed single deluges that ranged in size from 20 to 120 mm (82.3rd to >99.9th percentile of historical event size) on undisturbed grassland plots. We quantified pre‐ and postdeluge responses in soil moisture, soil respiration, and canopy greenness, as well as leaf water potential, growth, and flowering of the dominant grass species (Bouteloua gracilis). We also measured end of season above‐ and belowground net primary production (ANPP, BNPP). As expected, this water‐limited ecosystem responded strongly to the applied deluges, but surprisingly, most variables increased linearly with deluge size. We found little evidence for response thresholds within the range of deluge sizes imposed, at least during this dry year. Instead, response patterns reflected the linear increase in the duration of elevated soil moisture (2–22 days) with increasing event size. Flowering of B. gracilis and soil respiration responded particularly strongly to deluge size (14‐ and 4‐fold increases, respectively), as did ANPP and BNPP (~60% increase for both). Overall, our results suggest that this semiarid grassland will respond positively and linearly to predicted increases in deluge size, and that event sizes may need to exceed historical magnitudes, or occur during wet years, before responses saturate.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…At the end of the growing season, we assessed above‐ and belowground net primary production (ANPP, BNPP). Methods generally followed protocols in Post and Knapp (2020).…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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How big is big enough? Surprising responses of a semiarid grassland to increasing deluge size

Post

Knapp

2020

Global Change Biology

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Fluctuations in resource availability shape the competitive balance among non‐native plant species

Tao

Shen

Qin

et al. 2023

Ecological Applications

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Fluctuating resource availability plays a critical role in determining non‐native plant invasions through mediating the competitive balance between non‐native and native species. However, the impact of fluctuating resource availability on interactions among non‐native species remains largely unknown. This represents a barrier to understanding invasion mechanisms, particularly in habitats that harbor multiple non‐native species with different responses to fluctuating resource availability. To examine the responses of non‐native plant species to nutrient fluctuations, we compared the growth of each of 12 non‐native species found to be common in local natural areas to nutrients supplied at a constant rate or supplied as a single large pulse in a pot experiment. We found that seven species produced more biomass with pulsed nutrients compared to constant nutrients (hereafter “benefitting species”), while the other five species did not differ between nutrient enrichment treatments (hereafter “non‐benefitting species”). To investigate how nutrient fluctuations influence the interactions among non‐native plant species, we established experimental non‐native communities in the field with two benefitting and two non‐benefitting non‐native species. Compared with constant nutrient supply, the single large pulse of nutrient did not influence community biomass, but strongly increased the biomass and cover of the benefitting species and decreased those of the non‐benefitting species. Furthermore, the benefitting species had higher leaf N content and greater plant height when nutrients were supplied as a single large pulse than at a constant rate, whereas the non‐benefitting species showed no differences in leaf N content and were shorter when nutrients were supplied as a single large pulse than at a constant rate. Our results add to the growing evidence that the individual responses of non‐native species to nutrient fluctuation are species‐specific. More importantly, benefitting species were favored by nutrients coming in a pulse, while non‐benefitting ones were favored by nutrients coming constantly when they grew together. This suggests that nutrient fluctuations can mediate the competitive balance among non‐native plants and may thus determine their invasion success in a community harboring multiple non‐native plant species.

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Effects of nutrient pulses on exotic species shift from positive to neutral with decreasing water availability

Otieno

Shen

Zhang

et al. 2023

Ecological Applications

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Temporal fluctuation in nutrient availability generally promotes the growth of exotic plant species and has been recognized as an important driver of exotic plant invasions. However, little is known about how the impact of fluctuating nutrients on exotic species is dependent on the availability of other resources, although most ecosystems are experiencing dramatic variations in a wide variety of resources due to global change and human disturbance. Here, we explored how water availability mediates the effect of nutrient pulses on the growth of six exotic and six native plant species. We subjected individual plants of exotic and native species to well watered or water stressed conditions. For each level of water availability, we added equivalent amounts of nutrients at a constant rate, as a single large pulse, or in multiple small pulses. Under well watered conditions, nutrient pulses promoted exotic plant growth relative to nutrients supplied constantly, while they had no significant effect on natives. In contrast, under water stressed conditions, water deficiency inhibited the growth of all exotic and native species. More importantly, nutrient pulses did not increase plant growth relative to nutrients supplied constantly and these phenomena were observed for both exotic and native species. Taken together, our study shows that the impact of fluctuating nutrient availability on the growth of exotic plant species strongly depends on the variation of other resources, and that the positive effect of nutrient pulses under well watered conditions disappears under water stressed conditions. Our findings suggest that the variation in multiple resources may have complex feedback on exotic plant invasions and, therefore, it is critical to encompass multiple resources for the evaluation of fluctuating resource availability effects on exotic plant species. This will allow us to project the invasive trajectory of exotic plant species more accurately under future global change and human disturbance.

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The importance of extreme rainfall events and their timing in a semi‐arid grassland

Abstract: Warming air temperatures are intensifying the hydrologic cycle, resulting in altered weather patterns and more frequent extremes, such as droughts and large rainstorms (Donat, Lowry, Alexander,

Cited by 65 publications

References 103 publications

How big is big enough? Surprising responses of a semiarid grassland to increasing deluge size

How big is big enough? Surprising responses of a semiarid grassland to increasing deluge size

Fluctuations in resource availability shape the competitive balance among non‐native plant species

Effects of nutrient pulses on exotic species shift from positive to neutral with decreasing water availability

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