Griffin-Nolan Robert J, Felton Andrew J, Slette Ingrid J, Smith Melinda D, Knapp Alan K
Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA.
Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, 80523, USA.
Oecologia. 2023 Feb;201(2):311-322. doi: 10.1007/s00442-023-05315-y. Epub 2023 Jan 14.
Many plant traits respond to changes in water availability and might be useful for understanding ecosystem properties such as net primary production (NPP). This is especially evident in grasslands where NPP is water-limited and primarily determined by the traits of dominant species. We measured root and shoot morphology, leaf hydraulic traits, and NPP of four dominant North American prairie grasses in response to four levels of soil moisture in a greenhouse experiment. We expected that traits of species from drier regions would be more responsive to reduced water availability and that this would make these species more resistant to low soil moisture than species from wetter regions. All four species grew taller, produced more biomass, and increased total root length in wetter treatments. Each species reduced its leaf turgor loss point (TLP) in drier conditions, but only two species (one xeric, one mesic) maintained leaf water potential above TLP. We identified a suite of traits that clearly distinguished species from one another, but, surprisingly, these traits were relatively unresponsive to reduced soil moisture. Specifically, more xeric species produced thinner roots with higher specific root length and had a lower root mass fraction. This suggest that root traits are critical for distinguishing species from one another but might not respond strongly to changing water availability, though this warrants further investigation in the field. Overall, we found that NPP of these dominant grass species responded similarly to varying levels of soil moisture despite differences in species morphology, physiology, and habitat of origin.
许多植物性状会对水分可利用性的变化做出响应，可能有助于理解诸如净初级生产力（NPP）等生态系统属性。这在草原地区尤为明显，那里的NPP受水分限制，且主要由优势物种的性状决定。在一项温室实验中，我们测量了北美四种优势草原草的根和地上部分形态、叶片水力性状以及NPP，以响应四种土壤湿度水平。我们预计，来自较干旱地区的物种性状对水分可利用性降低的响应会更强，并且这会使这些物种比来自较湿润地区的物种更能抵抗低土壤湿度。在较湿润的处理条件下，所有四个物种都长得更高、产生了更多生物量并且总根长增加。在较干旱条件下，每个物种都降低了其叶片膨压损失点（TLP），但只有两个物种（一个旱生的，一个中生的）保持叶片水势高于TLP。我们确定了一组能明显区分物种的性状，但令人惊讶的是，这些性状对土壤湿度降低的响应相对较小。具体而言，更旱生的物种产生更细的根，具有更高的比根长且根质量分数较低。这表明根性状对于区分物种至关重要，但可能对变化的水分可利用性反应不强，不过这有待在野外进一步研究。总体而言，我们发现尽管这些优势草种在形态、生理和起源生境方面存在差异，但它们的NPP对不同水平的土壤湿度的响应相似。
