Sedgwick Reserve

09 Dec, 12 AM - 09 Dec, 11 AM

Main ideas: In California grasslands, several species produce aboveground biomass that dies in the spring, remains intact as thatch during the summer, and decomposes over the course of the following growing season. If the litter layer is thick at the beginning of the growing season, it may shade out seedlings of certain species such as Nassella pulchra, while simultaneously providing moister conditions under which Bromus diandrus seedlings can survive periods of drought following the first autumn rains. This study will focus on the decomposition of the B. diandrus and N. pulchra litter over the course of a year. We will follow the seasonal dynamics of litter decomposition to see if there are weather-driven patterns associated with its breakdown. We plan to look at how decomposition differs out in the open versus underneath oak tree canopies, and compare the decomposition of litter lying flat on the soil surface with that of litter that is perched above the grass canopy. We will also determine if litter decomposes more quickly when surrounded by live plants of the same species, different species, or in a mixed stand of B. diandrus and N. pulchra. Questions: 1. How quickly does litter decompose in California grasslands? Is this influenced by? * the species comprising the litter (B. diandrus vs. N. pulchra vs. mix)? * the location of the litter (under B. diandrus vs. under N. pulchra vs. under mix) * the position of the litter (flush with the ground vs. perched above the grass canopy)? * the presence of oak trees (litter under canopy vs. in open)? 2. How does litter chemistry change as it decomposes? Fieldwork: Litter was collected from two areas of the Reserve on November 29, 2007: an uplifted terrace of Quaternary stream deposits that was cleared in the 1940s and subsequently tilled (the ?Airstrip?), and the Mesa which has never been tilled. The Airstrip is a Thermic Typic Argixeroll (Fierer et al. 2003), but the Mesa soil has not been classified. The soil parent material at both sites is the Paso Robles formation, a weakly consolidated alluvium composed largely of Pleistocene-era shale (Dibblee 1966). A single collection site was established on the airstrip, while there were three distinct collection locals on the Mesa creating a total of four site replicates. Air temperature and precipitation data were obtained from a Campbell Tripod Weather Station equipped with a HMP35C Temperature and Relative Humidity Probe and a TE525 Tipping Bucket Rain Gauge. The weather station is located approximately 0.5 km away from the Airstrip, and 3 km away from the Mesa field site. Litter for the decomposition field study was homogenized by hand mixing, and allowed to air dry in the lab between the collection date and the installation date (December 18, 2007). Square bags measuring 7-10cm to a side were constructed from 1mm vinyl window screen mesh. Mesh was doubled over and either sewn together with thread, or melted together using an impulse sealer (get instrument info). Each bag was given a unique number to allow for easy identification, with the three replicates of each treatment type being sequentially numbered (i.e. bags numbered 1, 2, and 3 were replicates of a single litter type to be placed at the same field location). Numbered tags were affixed to bags using colored wire or zipties. A total of 1008 litter bags were constructed (see Table 1). The bags were filled with 0.50 ? 0.01 g of litter of the appropriate type, and sealed with the impulse sealer. Blanks for each of the six retrieval dates were created from bags containing no litter, and placed under the oak canopy and under Bromus diandrus both hanging and on the ground. Bags were placed in the field on December 18, 2007. Heavy rain fell throughout bag installation, and through the following night. Prior to bag installation, rainfall was minimal at Sedgwick Reserve (amounting to less that 1cm per event, with a total of three events between September X and December X, 2007). All litter bags were returned to the site where the litter they contained was originally collected. At each field location (under oak trees, B. diandrus, N. pulchra, and a mix of B. diandrus and N. pulchra), bags were separated into three groups, with each group containing one of the three replicate bags of each litter type. Each group was marked with a pin flag to facilitate bag retrieval later in the season. Extant litter was removed from the ground where bags were to be placed, and the litter was scattered on top of the bags following placement. Bags were affixed to the ground using 3" galvanized steel nails, and separated by a ~5 cm margin. Hanging bags were installed using bamboo stakes that were 50cm long and 0.5 cm in diameter. A small hole was drilled into the top of each stake, thin gauge wire was inserted through this hole and used to affix the bags on one corner. The bamboo was hammered into the ground so that the lowest hanging corner of each bag was 20 cm from the ground. Blanks were placed under oaks and under B. diandrus. Under oaks, there were three groups of 14 bags, and each group was arranged into two rows of seven bags. Under B. diandrus, there were three groups of 34 bags, six of which were hanging from bamboo stakes. Each group was arranged into five rows of six bags with one extra row of four bags. Under the N. pulchra stands, bags were snuggled under the N. pulchra canopy as much as possible, while in the mixed stands, groups of 18 bags were arranged into six rows of three and affixed to the ground (see Fig. 1). We propose the following pick-up schedule: 1 month- January 29 3 months- March 20's 6 months- May (end of growing season) 9 months- September (prior to first rains) 12 months- December 2008 18 months- May (end of growing season) Every bag pick-up date will be coupled with collection of thatch depth, vegetation height, soil moisture (%), light availability, and canopy density (under oak). Three replicates of each measurement will be taken at each treatment at each site, when possible measurements will be taken near the flag marking each plot in the field. Thatch depth and vegetation height were made by measuring the maxium height of vegetation in each plot. In the lab, litter collected from each site was cut into 3-5cm lengths using scissors. Everything aside from grass leaves and stalks was removed. Three subsamples of litter from each site were dried for one week at 35? C to obtain litter moisture contents. The dried samples were then homogenized using a wig-l-bug (Crescent, Maple Grove, MN) and beads. Samples were analyzed for carbon and nitrogen content using a NA1500 CN analyzer (Fisons Instruments, Milano, Italy) with an acetanilide standard.

Visit #16054 @Sedgwick Reserve

Approved

Under Project # 7679 | Research

The role of plant-fungi symbioses in furthering California grassland invasion

research_scientist - University of California, Santa Barbara

Reservation Members(s)

Group of 2 Graduate Student Dec 9, 2007 (1 days)
Sophie Parker Dec 9, 2007 (1 days)

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