A historical and comparative review of 50 years of root data collection in Puerto Rico

Abstract

Fine roots play an important role in plant nutrition, as well as in carbon, water, and nutrient cycling. Fine roots account for a third of terrestrial net primary production (NPP), and inclusion of their structure and function in global carbon models should improve predictions of ecosystem responses to climate change. However, studies focusing on underground plant components are much less frequent than those on aboveground structure. This is more marked in the tropics, where one-third of the planet's terrestrial NPP is produced. Some tropical forests have been more represented in the literature than others, as demonstrated in the collective studies in Puerto Rico. This Caribbean island's biodiversity, frequency of natural disturbances, ease of access to forests, and long-term plots have created an ideal place for the study of tropical ecological processes. This literature review emphasizes 50 years of root research and patterns revealed around Puerto Rico. The data in this review were compiled from scientific publications, conference reports, symposiums, and raw data shared by some researches. Emergent patterns include the shallow distribution of fine roots, the great variation in root biomass among different forest types, little variation in root phosphorus concentrations, the slow recovery of root biomass after Hurricane Hugo, and the fact that most data on roots come from the wet tropical Luquillo Experimental Forest, causing other habitat types to be underrepresented. This review also shows the gaps in knowledge about fine roots in the island's ecosystems, which should be used to promote and guide future studies. Abstract in Spanish is available with online material. K E Y W O R D S fine roots, hurricane, land-use history, luquillo experimental forest, rooting distribution, tropics S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section.

Bringing function to structure: Root–soil interactions shaping phosphatase activity throughout a soil profile in Puerto Rico

“…In our case, fine‐root biomass was concentrated in the top 20 cm, consistent with available P concentrations gradients (Lynch & Brown, 2001). Similarly, over 80% of root biomass was within the top 20 cm of the soil profile in a comprehensive review of roots in Puerto Rico (Yaffar & Norby, 2020). Global estimates using β to describe root depth distribution indicate that in tropical evergreen forests, where 70% of root biomass is in the upper 30 cm of the soil profile, β = 0.962 (Jackson et al., 1997).…”

“…Plant P acquisition within highly weathered tropical soils is determined in part by root expansion throughout the soil volume to capture available P and root physiological mechanisms that alter the soil environment to enhance P availability at the root surface where uptake occurs (Lambers et al., 2006). Prior work within the LEF shows that high fine‐root biomass is concentrated in the first few centimeters of mineral soil (Silver & Vogt, 1993; Yaffar & Norby, 2020), which could enable plants to capture nutrients renewed through litterfall (Silver et al., 1994). Global analysis also indicates that across forest types, 50 % of all roots are within the top 30 cm (Schenk & Jackson, 2002), perhaps due to the shallow distribution of bioavailable P in soil depth profiles (Jobbágy & Jackson, 2000).…”

“…Changes in soil conditions that alter microbial and root activity will subsequently influence soil and root PME as well. Both microbial biomass and root distribution both decrease with soil depth (Fierer et al., 2003; Schenk & Jackson, 2002; Stone et al., 2014; Yaffar & Norby, 2020), suggesting that soil PME and root PME will likely also decrease with soil depth. For soil PME, the decline in depth has been associated with decreasing quantity and quality of substrates.…”

“…The extensive research within the LEF describing factors that shape soil P distributions such redox and soil texture (Chacon et al., 2006; Silver et al., 1994, 2000) and root dynamics (Silver & Vogt, 1993; Yaffar & Norby, 2020) on Oxisol, Ultisol, and Inceptisol soils (Buss et al., 2010; Mage & Porder, 2013; Porder et al., 2015; Silver et al., 2000) makes it an ideal testing ground to connect PME activity to root traits and soil P distributions throughout depth and to improve how the P cycle is represented in ecosystem models. Model simulations indicate that soil organic P mineralization was overestimated in Oxisols because estimates of biochemical mineralization—phosphatase—were poorly constrained (Wang et al., 2010).…”

Photosynthetic and Respiratory Acclimation of Understory Shrubs in Response to in situ Experimental Warming of a Wet Tropical Forest

“…Importantly, hierarchical partitioning revealed that deeper soil moisture, even more so than vegetation temperature or shallow soil moisture, was the most influential climate variable determining variation in many gas exchange parameters (Supplementary Figure S11). Deeper, rather than shallow, soil moisture may have been a stronger driver because it was less variable in general ( Figure 2D; Kimball et al, 2018) likely because of less surface evaporation and fewer roots present to rapidly draw water from that soil depth (Yaffar and Norby, 2020). T opt increased as soil moisture decreased (Figures 8A,B), suggesting that neither species' T opt will likely be negatively affected by a drying climate.…”