DOI: 10.5061/dryad.3j9kd51g4
title: Climate change and defoliation interact to affect root length across northern temperate grasslands

description: 1. Grassland plants, especially their root systems, are dynamic and can
 buffer changes resulting from exposure to multiple stressors; however, the
 interactive stressor effects on root dynamics and associated aboveground
 growth are poorly understood. 2. Here, we examine the effects of changed
 precipitation and air temperature, and defoliation intensity on root
 length dynamics and aboveground biomass using the third year data from a
 multifactor experiment conducted across three northern temperate
 grasslands. 3. We found that root length was more sensitive to the changes
 in environmental and management conditions than root mass, demonstrating
 the importance of root length as an indicator of rapid root system
 changes. Across all sites, warming, altered precipitation, and defoliation
 intensity interacted to affect root length while aboveground biomass was
 only affected by defoliation intensity, indicating that the root system
 was more responsive than aboveground biomass when climatic conditions
 change. Overall, drought reduced root length, particularly under low
 defoliation intensity, as well as in combination with warming and heavy
 defoliation, highlighting the risk of additive effects of such
 environmental stresses. Across unclipped plots, aboveground biomass was
 positively associated with total root length, the latter of which further
 interacted with precipitation, to affect aboveground biomass. Compared to
 defoliated communities, non-defoliated plant communities exhibited a
 greater ability to maintain aboveground biomass under drought conditions
 via increases in root system efficiency (the amount of aboveground biomass
 produced per unit of root length invested). 4. Our results highlight the
 rapid change of root length in the face of interactive stressors. We
 postulate that the degree of stability in aboveground biomass is driven by
 the altered root system dynamics or species turnover. Future studies are
 warranted that more directly assess how root length responses under
 climate change impact other important plant traits in grasslands.
description: In May 2007, one minirhizotron tube (5
 cm inner diameter, 110 cm long) was installed in the center of each plot
 at a 45° angle from the soil surface. Tubes were made
 of clear cellulose acetate butyrate plastic and reached a depth of 40 cm.
 Image acquisition began in May 2009 (2
 years after installation) to allow fine roots to colonize the disturbed
 soil around the tubes. High-resolution images were acquired using a Bartz
 BTC 100X video microscope (Bartz Technology Corporation, Santa Barbara,
 California, USA) on May 11, June 2, June 22, July 15, August 10, and
 September 2 throughout the growing season. Images were
 categorized into two depth classes (0-20 and 20-40 cm) and digitally
 analyzed using WinRHIZO TRON software (Regent Instruments, Quebec,
 Canada). For each individual root observed, we noted the date of root
 appearance (i.e., birth) and disappearance (i.e., “death”) and measured
 root length and width (i.e., diameter) for each session the root was
 present. Roots were categorized into fourteen diameter classes
 (&lt;0.05,
 0.05-0.1, 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8,
 0.8-0.9, 0.9-1.0, 1.0-1.5, 1.5-2.0, &gt;2.0 mm) and measured after
 enlarging the images by a factor of 10.